Antireflection film

ABSTRACT

An antireflection film comprising silica particles and at least one binder compound, which has a silica particle content of 30% by weight or more, an arithmetic mean surface roughness (Ra) of not more than 2 nm, and a surface silicon atom content of 10 atom % or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antireflection film. Moreparticularly, the present invention is concerned with an antireflectionfilm comprising silica particles and at least one binder compound,wherein the silica particles are bound together through the at least onebinder compound, and wherein the antireflection film has a silicaparticle content of 30% by weight or more, an arithmetic mean surfaceroughness (Ra) of not more than 2 nm and a surface silicon atom contentof 10 atom % or more. The antireflection film of the present inventionnot only exhibits excellent antireflection performance, but also hasexcellent properties with respect to mechanical strength and abrasionresistance. Therefore, the antireflection film of the present inventionis very advantageous for coating various optical substrates (such aslenses of eye-glass and display screens).

2. Prior Art

Conventionally, as an antireflection film for coating an optical part,lenses of eye-glasses, a display screen or the like, there are known anantireflection film having a single-layer structure and anantireflection film having a multilayer structure. An antireflectionfilm having a single-layer structure or a double-layer structure hasdisadvantageously high reflectance. Therefore, it has been considered tobe more desirable to use an antireflection film having a laminatedstructure comprised of three or more different layers having differentrefractive indices. However, when such an antireflection film comprisedof three or more different layers is produced by any of the conventionalmethods, such as vacuum deposition and dip coating, disadvantages arecaused in that the production process is cumbersome and also theproductivity is low.

Therefore, studies have been made on antireflection films having asingle-layer structure or a double-layer structure, and it has beenfound that the refractive index of such a single-layer or double-layerantireflection film can be reduced when the antireflection filmsatisfies the conditions mentioned below. Thus, studies have been madefor developing a single-layer or double-layer film which satisfies suchconditions. Specifically, it is known that, in the case of an opticalpart comprising a substrate and, formed thereon, a single-layer film,the minimum value of the reflectance R of the optical part can beexpressed by the formula:

(n_(s)−n²)²/(n_(s)+n²)², wherein n_(s) represents the refractive indexof the substrate and n represents the refractive index of thesingle-layer film, with the proviso that n_(s)>n. When the minimum valueof the reflectance R is 0 (i.e., when (n_(s)−n²)²/(n_(s)+n²)²=0), itmeans that n=n_(s) ^(1/2). Therefore, it has been attempted to reducethe reflectance R by adjusting the refractive index n of thesingle-layer film to a value which is as close as possible to n_(s)^(1/2). Further, when it is difficult to adjust the refractive index nof the single-layer film to a value which is close to n_(s) ^(1/2), ithas also been attempted to reduce the reflectance R by a method in whicha high refraction layer having a high refractive index which is close ton² is formed between the substrate and the above-mentioned single-layerfilm having a refractive index n, to thereby obtain a double layerstructure.

At present, commercially available products of optical parts having anantireflection film have a minimum reflectance of about 2% in thevisible range. However, of these commercially available optical parts,the number of those optical parts having both a minimum reflectance of2% or less and practically satisfactory properties with respect tomechanical strength and durability, is very small. Therefore, it hasbeen desired to provide an antireflection film which can be easilyproduced and which has both a minimum reflectance of 2% or less,preferably a minimum reflectance of 1% or less and practicallysatisfactory properties with respect to mechanical strength anddurability.

On the other hand, for the purpose of providing an antireflection filmhaving an increased surface hardness and an anti-dazzling property(achieved by a light scattering property imparted to the surface of thefilm), it has been attempted to incorporate silica particles into thesurface portion of an antireflection film to thereby form minuteunevenness (i.e., minute dents and bumps) on the surface of theantireflection film. It is known that, by forming minute dents and bumpson the surface of the antireflection film in such way, there can beobtained, to some extent, the effect of improving the abrasionresistance of the antireflection film. The reason why such effect can beobtained is that the presence of the minute dents and bumps on thesurface of the antireflection film can decrease the practical contactarea between the antireflection film and an object which placed incontact with the surface of the antireflection film. However, anantireflection film having such a surface structure has posed a problemin that a stress applied to such a roughened surface of theantireflection film is inevitably mainly focused on the minute “peaktop” portions (i.e., dents) of the roughened surface and, hence, thesurface portion of the antireflection film is partially scraped offand/or the antireflection film is partially crushed in the thicknesswisedirection, leading to a partial lowering of thickness of theantireflection film, and this will cause an inadvertent change in thecolor tone of the antireflection film. When it is tried to solve thisproblem by a method in which the amount of silica particles used isincreased in an attempt to further increase the surface hardness of theantireflection film, the surface roughness of the antireflection film isfurther increased. This increase in the surface roughness poses problemsnot only in that there occurs an increase in the frictional resistancewhen the antireflection film is placed in contact with an object, butalso in that there occurs an increase in the coming off of silicaparticles from the surface of the antireflection film, thus leading toeven a lowering of the abrasion resistance (and not an increase in theabrasion resistance). Thus, in the conventional techniques, it is verydifficult to control the surface morphology and surface hardness of anantireflection film.

Unexamined Japanese Patent Application Laid-Open Specification Nos. Hei3-150501 and Hei 5-163464 disclose an antireflection film containingsilica particles and having minute dents and bumps on the surfacethereof. In these patent documents, these antireflection films aredescribed to show good results in the evaluation of the abrasionresistance. However, in these patent documents, the abrasion resistanceis evaluated simply by a method in which an antireflection film issubjected to rubbing using a stationery eraser. It is believed that, bysuch method, the practical performance of an antireflection film cannotbe satisfactorily evaluated.

Unexamined Japanese Patent Application Laid-Open Specification Nos. Hei11-292568 and 2000-256040 disclose an antireflection film containingsilica particles and having an arithmetic mean surface roughness (Ra) ofmore than 5 nm. In these patent documents, it is described that, whenthe antireflection film was subjected to measurement of the abrasionresistance by rubbing the antireflection films with a dry cloth, thewater contact angle of the antireflection film changed from 107° to100°. Such results of the evaluation cannot be considered to show thatthe antireflection film exhibits a satisfactory practical performance.

Unexamined Japanese Patent Application Laid-Open Specification Nos. Hei4-340902, Hei 7-48117, 2001-188104 and 2001-163906 disclose anantireflection film containing silica particles. However, in thetechniques of these patent documents, the use of silica particles issimply intended to improve the optical performance of the antireflectionfilm. In these patent documents, an antireflection film having a lowrefractive index and a low reflectance is obtained, but the abrasionresistance of the antireflection film is still unsatisfactory.

Unexamined Japanese Patent Application Laid-Open Specification No.2002-221603 discloses an antireflection film transfer structurecomprising a substrate having an arithmetic mean surface roughness (Ra)of from 2 to 150 nm and, laminated thereon, an antireflection layer tobe transferred, and also discloses an antireflection film obtained usingthe antireflection film transfer structure. In this patent document, thepurpose of adjusting the arithmetic mean surface roughness (Ra) of thesubstrate to a value within the range of from 2 to 150 nm is to improvethe uniformity of thickness of the antireflection film obtained. Thispatent document has no description about how the above-mentionedadjustment of the arithmetic mean surface roughness (Ra) contributes tothe strength of the antireflection film.

Further, it is known that when an antireflection film is caused to havea surface morphology having only few dents and bumps, i.e., a flatsurface, the abrasion resistance of the antireflection film is lowered.For example, International Publication No. WO03/083524 discloses anantireflection film containing silica particles, and has a descriptionthat, when the arithmetic mean surface roughness (Ra) of theantireflection film is less than 3 nm, a satisfactory abrasionresistance is not likely to be exhibited. Also, Unexamined JapanesePatent Application Laid-Open Specification No. 2002-79600 discloses anantireflection film containing silica particles, and has a descriptionthat, when the arithmetic mean surface roughness (Ra) of theantireflection film is less than 2 nm, a lowering of abrasion resistanceoccurs.

As described hereinabove, there has not yet been able to be obtained anantireflection film which not only exhibits excellent antireflectionperformance, but also has satisfactory properties with respect tomechanical strength and abrasion resistance.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive andintensive studies with a view toward solving the above-mentionedproblems accompanying the prior art. As a result, the present inventorshave unexpectedly found that the above objective can be attained by anantireflection film comprising silica particles and at least one bindercompound, wherein the silica particles are bound together through the atleast one binder compound, and wherein the antireflection film has asilica particle content of 30% by weight or more, an arithmetic meansurface roughness (Ra) of not more than 2 nm and a surface silicon atomcontent of 10 atom % or more. That is, it has surprising been found thatthe above-mentioned antireflection film not only exhibits excellentantireflection performance, but also has excellent properties withrespect to mechanical strength and abrasion resistance. The presentinvention has been completed, based on this finding.

Accordingly, it is an object of the present invention to provide anantireflection film which not only exhibits excellent antireflectionperformance, but also has excellent properties with respect tomechanical strength and abrasion resistance.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description takenin connection with the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagrammatic view showing the laminate structure of thetransfer foil C produced in Example 1;

FIG. 2 is a diagrammatic view showing the laminate structure of theoptical part D produced in Example 1;

FIG. 3 is a diagrammatic view showing the laminate structure of theoptical part E produced in Comparative Example 1;

FIG. 4 is a diagrammatic view showing the laminate structure of thetransfer foil G produced in Example 2;

FIG. 5 is a diagrammatic view showing the laminate structure of thelaminate H produced in Example 2;

FIG. 6 is a diagrammatic view showing the laminate structure of theoptical part I produced in Example 2;

FIG. 7 is a diagrammatic view showing the laminate structure of theoptical part J produced in Comparative Example 2;

FIG. 8 is a diagrammatic view showing the laminate structure of thetransfer foil L produced in Comparative Example 3;

FIG. 9 is a diagrammatic view showing the laminate structure of thelaminate M produced in Comparative Example 3; and

FIG. 10 is a diagrammatic view showing the laminate structure of theoptical part N produced in Comparative Example 3.

DESCRIPTION OF REFERENCE NUMERALS

-   1: Polyethylene terephthalate film (provisional substrate)-   2: Release layer-   3: Low refraction layer (antireflection film)-   4: High refraction layer having an antistatic effect-   5: Hard coat layer-   6: Adhesive layer-   7: Polymethyl methacrylate plate (optical substrate)-   8: Fluorine-containing surfactant layer-   9: Polyethylene terephthalate film (optical substrate)-   10: Ultraviolet-curable resin layer

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present invention, there is provided anantireflection film comprising silica particles and at least one bindercompound, wherein the silica particles are bound together through the atleast one binder compound,

the antireflection film having the following characteristics (a) to (c):

(a) a silica particle content of 30% by weight or more, based on theweight of the antireflection film,

(b) an arithmetic mean surface roughness (Ra) of not more than 2 nm, and

(c) a silicon atom content of 10 atom % or more, as measured by X-rayphotoelectron spectroscopy (XPS) with respect to the surface of theantireflection film.

For an easy understanding of the present invention, the essentialfeatures and various preferred embodiments of the present invention areenumerated below.

-   1. An antireflection film comprising silica particles and at least    one binder compound, wherein the silica particles are bound together    through the at least one binder compound,

the antireflection film having the following characteristics (a) to (c):

(a) a silica particle content of 30% by weight or more, based on theweight of the antireflection film,

(b) an arithmetic mean surface roughness (Ra) of not more than 2 nm, and

(c) a silicon atom content of 10 atom % or more, as measured by X-rayphotoelectron spectroscopy (XPS) with respect to the surface of theantireflection film.

-   2. The antireflection film according to item 1 above, wherein the at    least one binder compound is a polymer having functional groups, and    wherein the silica particles are covalently bonded to the functional    groups of the polymer.-   3. The antireflection film according to item 2 above, wherein the    molar ratio of the functional groups of the polymer to the silicon    atoms present in the silica particles is from 0.01 to 5.-   4. The antireflection film according to any one of items 1 to 3    above, wherein the silica particles comprise at least one stringy    silica particle selected from the group consisting of a moniliform    silica string and a fibrous silica particle.-   5. The antireflection film according to item 4 above, wherein the at    least one stringy silica particle is present in an amount of 50% by    weight or less, based on the weight of the antireflection film.-   6. The antireflection film according to any one of items 1 to 5    above, which is porous and has a porosity of from 3 to 50% by    volume.-   7. An antireflection laminate film comprising a high refraction film    and, laminated thereon directly or indirectly, the antireflection    film of any one of items 1 to 6 above, wherein the high refraction    film has a refractive index higher than the refractive index of the    antireflection film.-   8. The antireflection laminate film according to item 7 above,    wherein the high refraction film comprises:

particles of at least one metal oxide comprising at least one metalselected from the group consisting of titanium, zirconium, zinc, cerium,tantalum, yttrium, hafnium, aluminum, magnesium, indium, tin,molybdenum, antimony and gallium, and

at least one binder compound,

wherein the particles of at least one metal oxide are bound togetherthrough the at least one binder compound.

-   9. An optical part comprising an optical substrate and, laminated    thereon, the antireflection film of any one of items 1 to 6 above.-   10. The optical part according to item 9 above, wherein the optical    substrate is a transparent resin substrate.-   11. The optical part according to item 9 above or 10, which has a    minimum reflectance of not more than 2% within the visible light    range.-   12. The optical part according to any one of items 9 to 11 above,    which has a pencil hardness of 2H or more.-   13. The optical part according to any one of items 9 to 12 above,    which is obtained by a method comprising:

(1) forming the antireflection film of any one of items 1 to 6 above ona provisional substrate having releasability with respect to theantireflection film, to thereby obtain a laminate (i);

(2) laminating an optical substrate on the antireflection film of thelaminate (i) to obtain a laminate (ii); and

(3) delaminating the provisional substrate from the laminate (ii) toobtain an optical part.

-   14. An optical part comprising an optical substrate and, laminated    thereon, the antireflection laminate film of item 7 or 8 above.-   15. The optical part according to item 14 above, wherein the optical    substrate is a transparent resin substrate.-   16. The optical part according to item 14 or 15 above, which has a    minimum reflectance of not more than 2% within the visible light    range.-   17. The optical part according to any one of items 14 to 16 above,    which has a pencil hardness of 2H or more.-   18. The optical part according to any one of items 14 to 17 above,    which is obtained by a method comprising:

(1) forming the antireflection film of any one of items 1 to 6 above ona provisional substrate having releasability with respect to theantireflection film, to thereby obtain a laminate (I);

(2) laminating a high refraction film on the antireflection film of thelaminate (I) to obtain a laminate (II);

(3) laminating an optical substrate on the high refraction film of thelaminate (II) to obtain a laminate (III); and

(4) delaminating the provisional substrate from the laminate (III) toobtain an optical part.

Hereinbelow, the present invention is described in detail.

The antireflection film of the present invention comprises silicaparticles and at least one binder compound, wherein the silica particlesare bound together through the at least one binder compound.

In the present invention, the thickness of the antireflection film isgenerally from 50 to 1,000 nm, preferably from 50 to 500 nm, morepreferably from 60 to 200 nm. When the antireflection film has athickness of less than 50 nm or more than 1,000 nm, the antireflectioneffect on light in the visible light range may be lowered.

In the present invention, it is necessary that the antireflection filmhave a silica particle content of 30% by weight or more, preferably from30 to 95% by weight, more preferably from 40 to 90% by weight, stillmore preferably from 50 to 80% by weight. By virtue of the silicaparticle content of 30% by weight or more, it becomes possible to obtainan antireflection film having a satisfactory strength. Further, in somecases, the silica particle content of 30% by weight or more provides afurther advantage in that the refractive index of the antireflectionfilm can be further lowered by the presence of microvoids formed betweenmutually adjacent silica particles. When the silica particle content isless than 30% by weight, problems are likely to be caused not only inthat the strength of the antireflection film becomes unsatisfactory, butalso in that mechanical properties (such as abrasion resistance) are notsatisfactorily improved. On the other hand, when the silica particlecontent is more than 95% by weight, problems are likely to be caused inthat mechanical properties (such as abrasion resistance) are notsatisfactorily improved.

In the present invention, preferred examples of methods for measuringthe silica particle content of the antireflection film include a methodin which an antireflection film is analyzed by X-ray photoelectronspectroscopy (XPS) while scraping the antireflection film by sputtering.

With respect to the shape of the silica particles used in theantireflection film, there is no particular limitation, and there can beused any of spherical silica particles, plate-shaped silica particles,needle-shaped silica particles, stringy silica particles and botryoidalsilica particles.

The term “stringy silica particles” means strings of silica (hereinafterreferred to as moniliform silica strings) in which a plurality of silicaparticles (such as spherical silica particles, plate-shaped silicaparticles and needle-shaped silica particles) are linked in rosary form,short-fibrous silica particles disclosed in Unexamined Japanese PatentApplication Laid-Open Specification No. 2001-188104, or the like. Thesestringy silica particles may be used individually or in combination.Further, these stringy silica particles may be linear or branched.

Further, the term “botryoidal silica particles” means a botryoidalcoalescent cluster of a plurality of silica particles (such as sphericalsilica particles, plate-shaped silica particles, needle-shaped silicaparticles or the like).

In the present invention, the term “spherical silica particle” means asilica particle in which the ratio of the longest diameter (major axis)of the particle to the shortest diameter (minor diameter) as measured ina direction perpendicular to the longest diameter is less than 1.5.Silica particles which do not satisfy the above-mentioned ratio areregarded as non-spherical silica particles. The shape of silicaparticles can be confirmed by, for example, observation using atransmission electron microscope.

In the present invention, it is preferred to use non-spherical silicaparticles (i.e., plate-shaped silica particles, needle-shaped silicaparticles, stringy silica particles, botryoidal silica particles or thelike) because microvoids are more likely to be formed between mutuallyadjacent non-spherical silica particles, thereby lowering the refractiveindex of the antireflection film.

When spherical silica particles, plate-shaped silica particles orneedle-shaped silica particles are used, it is preferred that theaverage particle diameter is within the range of from 10 to 200 nm. Theterm “average particle diameter” means a value obtained by the followingformula:

average particle diameter (unit: nm)=(2,720/specific surface area),wherein the specific surface area (m²/g) is measured by a conventionalnitrogen adsorption method (BET method) (see Unexamined Japanese PatentApplication Laid-Open Specification No. Hei 1-317115). When the averageparticle diameter of the silica particles is less than 10 nm, there is apossibility that it becomes difficult to obtain an antireflection filmhaving satisfactory strength. On the other hand, when the averageparticle diameter of the silica particles is more than 200 nm, there isa possibility that the arithmetic mean surface roughness (Ra) of theantireflection film becomes large, so that haze tends to occur and theresolution of an image which is observed through the antireflection filmtends to be lowered.

When the stringy silica particles are used, it is especially preferredto use moniliform silica strings having an average length of from 30 to200 nm, wherein each moniliform silica string comprises silica particles(such as spherical silica particles, plate-shaped silica particles, andneedle-shaped silica particles) having an average particle diameter offrom 5 to 30 nm, more advantageously from 10 to 30 nm, the silicaparticles being linked in rosary form. The term “average length” means avalue as measured by the dynamic light scattering method. The averagelength can be measured by, for example, a dynamic light scatteringmethod described in “Journal of Chemical Physics”, Vol. 57, No.11, p.4,814 (1972).

When the average particle diameter of the silica particles constitutingthe moniliform silica strings is less than 10 nm, there is a possibilitythat it becomes difficult to obtain an antireflection film havingsatisfactory strength. On the other hand, when the average particlediameter of the silica particles constituting the moniliform silicastrings is more than 30 nm, there is a possibility that the arithmeticmean surface roughness (Ra) of the antireflection film becomes large, sothat haze tends to occur and the resolution of an image which isobserved through the antireflection film tends to be lowered, thuslowering the visibility of the image. Further, when the average lengthof the moniliform silica strings is less than 30 nm, there is apossibility that it becomes difficult to obtain an antireflection filmhaving satisfactory strength. On the other hand, when the average lengthof the moniliform silica strings is more than 200 nm, there is also apossibility that the arithmetic mean surface roughness (Ra) of theantireflection film becomes large, so that haze tends to occur and theresolution (i.e., definition) of an image which is observed through theantireflection film tends to be lowered, thus lowering the visibility ofthe image.

In the present invention, the use of the stringy silica particles ispreferred in that the strength of the antireflection film can beimproved. Specifically, the use of the stringy silica particles isadvantageous in that it becomes easy to cause the silica particles to bepresent at a position near the surface of the antireflection film, inthat the silica particles become less likely to come off from thesurface of the antireflection film, and in that the number of points atwhich silica particles are in contact and linked with each other becomeslarge. As stringy silica particles, the moniliform silica strings areespecially preferred, and it is most preferred to use a moniliformsilica string having a two-dimensionally or three-dimensionally curvedform. Specific examples of moniliform silica strings include Snowtex®OUP, Snowtex® UP, Snowtex® PS-S, Snowtex® PS-SO, Snowtex® PS-M, Snowtex®PS-MO (each manufactured and sold by Nissan Chemical Industries, Ltd.,Japan), and Fine Cataloid F-120 (manufactured and sold by Catalysts &Chemicals Industries, Ltd., Japan). These moniliform silica strings havea dense skeleton of silica, and have a three-dimensionally curved form,and, thus, are especially preferred in the present invention.

In the present invention, when stringy silica particles are used, thereis no particular limitation with respect to the content of stringysilica particles in the antireflection film. When the content of stringysilica particles in the antireflection film is relatively large, thevolume of the voids formed in the antireflection film becomes large, sothat the refractive index of the antireflection film can be reduced. Onthe other hand, when the content of stringy silica particles in theantireflection film is relatively small, the unevenness of the surfaceof the antireflection film is lowered, so that the arithmetic meansurface roughness (Ra) of the antireflection film can be reduced. Thecontent of stringy silica particles in the antireflection film ispreferably from 1 to 90% by weight, more preferably from 10 to 70% byweight, still more preferably from 20 to 50% by weight. When the contentof the silica strings in the antireflection film is more than 90% byweight, the arithmetic mean surface roughness (Ra) may become more than2 nm.

Further, when the stringy silica particles are used in combination withsilica particles other than stringy silica particles, there is noparticular limitation with respect to the weight ratio of stringy silicaparticles to silica particles other than stringy silica. However, it ispreferred that the weight ratio of stringy silica particles to silicaparticles other than stringy silica particles is within the range offrom 0.01 to 100, more advantageously from 0.1 to 10, still moreadvantageously from 0.3 to 3.

The antireflection film of the present invention comprises the silicaparticles and at least one binder compound, wherein the silica particlesare bound together through the at least one binder compound.

As a binder compound, there can be used either of a binder compoundwhich forms a chemical bond with silica particles and a binder compoundwhich does not form a chemical bond with silica particles. However,preferred is a binder compound which forms a chemical bond with silicaparticles. Examples of preferred binder compounds are as follows.

-   (1) Hydrolysable silanes, such as tetramethoxysilane,    tetraethoxysilane, tetra(n-propoxy)silane, tetra(i-propoxy)silane,    tetra(n-butoxy)silane, tetra-sec-butoxysilane,    tetra-tert-butoxysilane, trimethoxysilane, triethoxysilane,    methyltrimethoxysilane, methyltriethoxysilane,    ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane,    propyltriethoxysilane, isobutyltriethoxysilane,    cyclohexyltrimethoxysilane, phenyltrimethoxysilane,    phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane,    allyltrimethoxysilane, allyltriethoxysilane,    methyltri(n-propoxy)silane, methyltri(iso-propoxy)silane,    methyltri(n-butoxy)silane, methyltri(sec-butoxy)silane,    methyltri(tert-butoxy)silane, ethyltri(n-propoxy)silane,    ethyltri(iso-propoxy)silane, ethyltri(n-butoxy)silane,    ethyltri(sec-butoxy)silane, ethyltri(tert-butoxy)silane,    n-propyltri(n-propoxy)silane, n-propyltri(iso-propoxy)silane,    n-propyltri(n-butoxy)silane, n-propyltri(sec-butoxy)silane,    n-propyltri(tert-butoxy)silane, i-propyltrimethoxysilane,    i-propyltriethoxysilane, i-propyltri(n-propoxy)silane,    i-propyltri(iso-propoxy)silane, i-propyltri(n-butoxy)silane,    i-propyltri(sec-butoxy)silane, i-propyltri(tert-butoxy)silane,    n-butyltrimethoxysilane, n-butyltriethoxysilane,    n-butyltri(n-propoxy)silane, n-butyltri(iso-propoxy)silane,    n-butyltri(n-butoxy)silane, n-butyltri(sec-butoxy)silane,    n-butyltri(tert-butoxy)silane, n-butyltriphenoxysilane,    sec-butyltrimethoxysilane, sec-butyltri(n-propoxy)silane,    sec-butyltri(iso-propoxy)silane, sec-butyltri(n-propoxy)silane,    sec-butyltri(sec-propoxy)silane, sec-butyltri(tert-butoxy)silane,    t-butyltrimethoxysilane, t-butyltriethoxysilane,    t-butyltri(n-propoxy)silane, t-butyltri(iso-propoxy)silane,    t-butyltri(n-butoxy)silane, t-butyltri(sec-butoxy)silane,    t-butyltri(tert-butoxy)silane, phenyltri(n-propoxy)silane,    phenyltri(iso-propoxy)silane, phenyltri(n-butoxysilane),    phenyltri(sec-butoxy)silane, phenyltri(tert-butoxy)silane,    dimethoxysilane, diethoxysilane, methyldimethoxysilane,    methyldiethoxysilane, dimethyldimethoxysilane,    dimethyldiethoxysilane, dimethyldi(n-propoxy)silane,    dimethyldi(i-propoxy)silane, dimethyldi(n-butoxy)silane,    dimethyldi(sec-butoxy)silane, dimethyldi(tert-butoxy)silane,    diethyldimethoxysilane, diethyldiethoxysilane,    diethyldi(n-propoxy)silane, diethyldi(i-proposy)silane,    diethyldi(n-butoxy)silane, diethyldi(sec-butoxy)silane,    diethyldi(tert-butoxy)silane, diphenyldimethoxysilane,    diphenyldiethoxysilane, diphenyldi(n-propoxy)silane,    diphenyldi(i-propoxy)silane, diphenyldi(n-butoxy)silane,    diphenyldi(sec-butoxy)silane, diphenyldi(tert-butoxy)silane,    methylethyldimethoxysilane, methylethyldiethoxysilane,    methylethyldi(n-propoxy)silane, methylethyldi(i-propoxy)silane,    mehtylethyldi(n-butoxy)silane, methylethyldi(sec-butoxy)silane,    methylethyldi(tert-butoxy)silane, methylpropyldimethoxysilane,    methylpropyldiethoxysilane, methylpropyldi(n-propoxy)silane,    methylpropyldi(i-propoxy)silane, methylpropyldi(n-butoxy)silane,    methylpropyldi(sec-butoxy)silane, methylpropyldi(tert-butoxy)silane,    methylphenyldimethoxysilane, methylphenyldiethoxysilane,    methylphenyldi(n-propoxy)silane, methylphenyldi(i-propoxy)silane,    methylphenyldi(n-butoxy)silane, methylphenyldi(sec-butoxy)silane,    methylphenyldi(tert-butoxy)silane, ethylphenyldimethoxysilane,    ethylphenyldiethoxysilane, ethylphenyldi(n-propoxy)silane,    ethylphenyldi(i-propoxy)silane, ethylphenyldi(n-butoxy)silane,    ethylphenyldi(sec-butoxy)silane, ethylphenyldi(tert-butoxy)silane,    methylvinyldimethoxysilane, methylvinyldiethoxysilane,    methylvinyldi(n-propoxy)silane, methylvinyldi(i-propoxy)silane,    methylvinyldi(n-butoxy)silane, methylvinyldi(sec-butoxy)silane,    methylvinyldi(tert-butoxy)silane, divinyldimethoxysilane,    divinyldiethoxysilane, divinyldi(n-propoxy)silane,    divinyldi(i-propoxy)silane, divinyldi(n-butoxy)silane,    divinyldi(sec-butoxy)silane, divinyldi(tert-butoxy)silane,    methoxysilane, ethoxysilane, methylmethoxysilane,    methylethoxysilane, dimethylmethoxysilane, dimethylethoxysilane,    trimethylmethoxysilane, trimethylethoxysilane,    trimethyl(n-propoxy)silane, trimethyl(i-propoxy)silane,    trimethyl(n-butoxy)silane, trimethyl(sec-butoxy)silane,    trimethyl(tert-butoxy)silane, triethylmethoxysilane,    triethylethoxysilane, triethyl(n-propoxy)silane,    triethyl(i-propoxy)silane, triethyl(n-butoxy)silane,    triethyl(sec-butoxy)silane, triethyl(tert-butoxy)silane,    tripropylmethoxysilane, tripropylethoxysilane,    tripropyl(n-propoxy)silane, tripropyl(i-propoxy)silane,    tripropyl(n-butoxy)silane, tripropyl(sec-butoxy)silane,    tripropyl(tert-butoxy)silane, triphenylmethoxysilane,    triphenylethoxysilane, triphenyl(n-propoxy)silane,    triphenyl(i-propoxy)silane, triphenyl(n-butoxy)silane,    triphenyl(sec-butoxy)silane, triphenyl(tert-butoxy)silane,    methyldiethylmethoxysilane, methyldiethylethoxysilane,    methyldiethyl(n-propoxy)silane, methyldiethyl(i-propoxy)silane,    methyldiethyl(n-butoxy)silane, methyldiethyl(sec-butoxy)silane,    methyldiethyl(tert-butoxy)silane, methyldipropylmethoxysilane,    methyldipropylethoxysilane, methyldipropyl(n-propoxy)silane,    methyldipropyl(i-propoxy)silane, methyldipropyl(n-butoxy)silane,    methyldipropyl(sec-butoxy)silane, methyldipropyl(tert-butoxy)silane,    methyldiphenylmethoxysilane, methyldiphenylethoxysilane,    methyldiphenyl(n-propoxy)silane, methyldiphenyl(i-propoxy)silane,    methyldiphenyl(n-butoxy)silane, methyldiphenyl(sec-butoxy)silane,    methyldiphenyl(tert-butoxy)silane, ethyldimethylmethoxysilane,    ethyldimethylethoxysilane, ethyldimethyl(n-propoxy)silane,    ethyldimethyl(i-propoxy)silane, ethyldimethyl(n-butoxy)silane,    ethyldimethyl(sec-butoxy)silane, ethyldimethyl(tert-butoxy)silane,    ethyldipropylmethoxysilane, ethyldipropylethoxysilane,    ethyldipropyl(n-propoxy)silane, ethyldipropyl(i-propoxy)silane,    ethyldipropyl(n-butoxy)silane, ethyldipropyl(sec-butoxy)silane,    ethyldipropyl(tert-butoxy)silane, ethyldiphenylmethoxysilane,    ethyldiphenylethoxysilane, ethyldiphenyl(n-propoxy)silane,    ethyldiphenyl(i-propoxy)silane, ethyldiphenyl(n-butoxy)silane,    ethyldiphenyl(sec-butoxy)silane, ethyldiphenyl(tert-butoxy)silane,    propyldimethylmethoxysilane, propyldimethylethoxysilane,    propyldimethyl(n-propoxy)silane, propyldimethyl(i-propoxy)silane,    propyldimethyl(n-butoxy)silane, propyldimethyl(sec-butoxy)silane,    propyldimethyl (tert-butoxy)silane, propyldiethylmethoxysilane,    propyldiethylethoxysilane, propyldiethyl(n-propoxy)silane,    propyldiethyl(i-propoxy)silane, propyldiethyl(n-butoxy)silane,    propyldiethyl(sec-butoxy)silane, propyldiethyl(tert-butoxy)silane,    propyldiphenylmethoxysilane, propyldiphenylethoxysilane,    propyldiphenyl(n-propoxy)silane, propyldiphenyl(i-propoxy)silane,    propyldiphenyl(n-butoxy)silane, propyldiphenyl(sec-butoxy)silane,    propyldiphenyl(tert-butoxy)silane, phenyldimethylmethoxysilane,    phenyldimethylethoxysilane, phenyldimethyl(n-propoxy)silane,    phenyldimethyl(i-propoxy)silane, phenyldimethyl(n-butoxy)silane,    phenyldimethyl(sec-butoxy)silane, phenyldimethyl(tert-butoxy)silane,    phenyldiethylmethoxysilane, phenyldiethylethoxysilane,    phenyldiethyl(n-propoxy)silane, phenyldiethyl(i-propoxy)silane,    phenyldiethyl(n-butoxy)silane, phenyldiethyl(sec-butoxy)silane,    phenyldiethyl(tert-butoxy)silane, phenyldipropylmethoxysilane,    phenyldipropylethoxysilane, phenyldipropyl(n-propoxy)silane,    phenyldipropyl(i-propoxy)silane, phenyldipropyl(n-butoxy)silane,    phenyldipropyl (sec-butoxy)silane,    phenyldipropyl(tert-butoxy)silane, trivinylmethoxysilane,    trivinylethoxysilane, trivinyl(n-propoxy)silane,    trivinyl(i-propoxy)silane, trivinyl (n-butoxy)silane,    trivinyl(sec-butoxy)silane, trivinyl(tert-butoxy)silane,    vinyldimethylmethoxysilane, vinyldimethylethoxysilane,    vinyldimethyl(n-propoxy)silane, vinyldimethyl(i-propoxy)silane,    vinyldimethyl(n-butoxy)silane, vinyldimethyl(sec-butoxy)silane,    vinyldimethyl(tert-butoxy)silane, vinyldiethylmethoxysilane,    vinyldiethylethoxysilane, vinyldiethyl(n-propoxy)silane,    vinyldiethyl(i-propoxy)silane, vinyldiethyl(n-butoxy)silane,    vinyldiethyl(sec-butoxy)silane, vinyldiethyl(tert-butoxy)silane,    vinyldipropylmethoxysilane, vinyldipropylethoxysilane,    vinyldipropyl(n-propoxy)silane, vinyldipropyl(i-propoxy)silane,    vinyldipropyl(n-butoxy)silane, vinyldipropyl(sec-butoxy)silane,    vinyldipropyl(tert-butoxy)silane, bis(trimethoxysilyl)methane,    bis(triethoxysilyl)methane, bis(triphenoxysilyl)methane,    bis(trimethoxysilyl)ethane, bis(triethoxysilyl)ethane,    bis(triphenoxysilyl)ethane, 1,3-bis(trimethoxysilyl)propane, 1,3-bis    (triethoxysilyl)propane, 1,3-bis(triphenoxysilyl)propane,    1,4-bis(trimethoxysilyl)benzene, 1,4-bis(triethoxysilyl)benzene,    hexamethoxydisiloxane, hexaethoxydisiloxane, hexaphenoxydisiloxane,    1,1,1,3,3-pentamethoxy-3-methyldisiloxane,    1,1,1,3,3-pentaethoxy-3-methyldisiloxane,    1,1,1,3,3-pentamethoxy-3-phenyldisiloxane,    1,1,1,3,3-pentaethoxy-3-phenyldisiloxane,    1,1,3,3-tetramethoxy-1,3-dimethyldisiloxane,    1,1,3,3-tetraethoxy-1,3-dimethyldisiloxane,    1,1,3,3-tetramethoxy-1,3-diphenyldisiloxane,    1,1,3,3-tetraethoxy-1,3-diphenyldisiloxane,    1,1,3-trimethoxy-1,3,3-trimethyldisiloxane,    1,1,3-triethoxy-1,3,3-trimethyldisiloxane,    1,1,3-trimethoxy-1,3,3-triphenyldisiloxane,    1,1,3-triethoxy-1,3,3-triphenyldisiloxane,    1,3-dimethoxy-1,1,3,3-tetramethyldisiloxane,    1,3-diethoxy-1,1,3,3-tetramethyldisiloxane,    1,3-dimethoxy-1,1,3,3-tetraphenyldisiloxane,    1,3-diethoxy-1,1,3,3-tetraphenyldisiloxane, 1,3-dimethoxy    1,1,3,3-tetramethyldisiloxane,    1,3-diethoxy-1,1,3,3-tetramethyldisiloxane,    1,3-dimethoxy-1,1,3,3-tetraphenyldisiloxane,    1,3-diethoxy-1,1,3,3-tetraphenyldisiloxane,    3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane,    3-hydroxypropyltrimethoxysilane, 3-hydroxypropyltriethoxysilane,    3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,    trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane,    3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane,    N-(2-aminoethyl)-3-aminopropyltriethoxysilane,    N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, tetraacetoxysilane,    tetrakis(trichloroacetoxy)silane, tetrakis(trifluoroacetoxy)silane,    triacetoxysilane, tris(trichloroacetoxy)silane,    tris(trifluoroacetoxy)silane, methyltriacetoxysilane,    methyltris(trichloroacetoxy)silane,    methyltris(trifluoroacetoxy)silane, phenyltriacetoxysilane,    phenyltris(trichloroacetoxy)silane,    phenyltris(trifluoroacetoxy)silane, methyldiacetoxysilane,    methylbis(trichloroacetoxy)silane,    methylbis(trifluoroacetoxy)silane, phenyldiacetoxysilane,    phenylbis(trichloroacetoxy)silane,    phenylbis(trifluoroacetoxy)silane, dimethyldiacetoxysilane,    dimethylbis(trichloroacetoxy)silane,    dimethylbis(trifluoroacetoxy)silane, methylphenyldiacetoxysilane,    methylphenylbis(trichloroacetoxy)silane,    methylphenylbis(trifluoroacetoxy)silane, diphenyldiacetoxysilane,    diphenylbis(trichloroacetoxy)silane,    diphenylbis(trifluoroacetoxy)silane, methylacetoxysilane,    methyl(trichloroacetoxy)silane, methyl(trifluoroacetoxy)silane,    phenylacetoxysilane, phenyl(trichloroacetoxy)silane,    phenyl(trifluoroacetoxy)silane, dimethylacetoxysilane,    dimethyl(trichloroacetoxy)silane, dimethyl(trifluoroacetoxy)silane,    diphenylacetoxysilane, diphenyl(trichloroacetoxy)silane,    diphenyl(trifluoroacetoxy)silane, trimethylacetoxysilane,    trimethyl(trichloroacetoxy)silane,    trimethyl(trifluoroacetoxy)silane, triphenylacetoxysilane,    triphenyl(trichloroacetoxy)silane,    triphenyl(trifluoroacetoxy)silane, tetrachlorosilane,    tetrabromosilane, tetrafluorosilane, trichlorosilane,    tribromosilane, trifluorosilane, methyltrichlorosilane,    methyltribromosilane, methyltrifluorosilane, phenyltrichlorosilane,    phenyltribromosilane, phenyltrifluorosilane, methyldichlorosilane,    methyldibromosilane, methyldifluorosilane, phenyldichlorosilane,    phenyldibromosilane, phenyldifluorosilane, dimethyldichlorosilane,    dimethyldibromosilane, dimethyldifluorosilane,    methylphenyldichlorosilane, methylphenyldibromosilane,    methylphenyldifluorosilane, diphenyldichlorosilane,    diphenyldibromosilane, diphenyldifluorosilane, methylchlorosilane,    methylbromosilane, methylfluorosilane, phenylchlorosilane,    phenylbromosilane, phenylfluoro-silane, dimethylchlorosilane,    dimethylbromosilane, dimethylfluorosilane, diphenylchlorosilane,    diphenylbromosilane, diphenylfluorosilane, trimethylchlorosilane,    trimethylbromosilane, trimethylfluorosilane, triphenylchlorosilane,    triphenylbromosilane and triphenylfluorosilane; or a partial    hydrolysis product and/or a dehydration-condensation product of any    of the above-mentioned compounds (wherein when any one of these    compounds exemplified in this item (1) is used as a binder compound,    it is preferred that the binder compound is three-dimensionally    cross-linked through siloxane linkages in the antireflection film).-   (2) Hydrolyzable silanes having, in a molecule thereof, a    polymerizable functional group and a functional group capable of    forming a covalent bond with silica particles, such as    3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane,    3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane,    3-methacryloxypropyltrimethoxysilane,    3-methacryloxypropyltriethoxysilane,    3-acryloxypropyltriacetoxysilane,    3-acryloxypropyltris(trichloroacetoxy)silane,    3-acryloxypropyltris(trifluoroacetoxy)silane,    3-methacryloxypropyltriacetoxysilane,    3-methacryloxypropyltris(trichloroacetoxy)silane,    3-methacryloxypropyltris(trifluoroacetoxy)silane,    3-glycidoxypropyltriacetoxysilane,    3-glycidoxypropyltris(trichloroacetoxy)silane,    3-glycidoxypropyltris(trifluoroacetoxy)silane,    3-acryloxypropyltrichlorosilane, 3-acryloxypropyltribromosilane,    3-acryloxypropyltrifluorosilane,    3-methacryloxypropyltrichlorosilane,    3-methacryloxypropyltribromosilane,    3-methacryloxypropyltrifluorosilane,    3-glycidoxypropyltrichlorosilane, 3-glycidoxypropyltribromosilane,    3-glycidoxypropyltrifluorosilane,    3-glycidoxypropylmethyldimethoxysilane,    3-glycidoxypropylmethyldiethoxysilane,    3-glycidoxypropyldimethylmethoxysilane,    3-glycidoxypropyldimethylethoxysilane,    3-methacryloxypropylmethyldimethoxysilane,    3-methacryloxypropylmethyldiethoxysilane,    3-methacryloxypropyldimethylmethoxysilane,    3-methacryloxypropyldimethylethoxysilane,    3-methacryloxypropyltris(methoxyethoxy)silane,    3-methacryloxypropylmethyldichlorosilane,    3-methacryloxypropyldimethylchlorosilane,    3-methacryloxypropylsilatrane, 3-methacryloxypropyltripropoxysilane,    O-methacryloxyethyl-N-triethoxysilylpropylurethane,    N-(3-methacryloxy-2-hydroxypropyl)-3-aminopropyltrietox ysilane,    3-mercaptopropyltrimetoxysilane, 3-mercaptopropyltrietoxysilane,    3-mercaptopropylmethyldimethoxysilane,    3-mercaptopropylmethyldiethoxysilane,    3-mercaptopropyldimethylmethoxysilane and    3-mercaptopropyldimethylethoxysilane; or a partial hydrolysis    product and/or a dehydration-condensation product of any of the    above-mentioned compounds (wherein when any one of these compounds    exemplified in this item (2) is used as a binder compound, it is    preferred that the binder compound is three-dimensionally    cross-linked through siloxane linkages or the polymerizable    functional group of the binder compound is polymerized in the    antireflection film, more advantageously not only is the binder    compound three-dimensionally cross-linked through siloxane linkages    in the antireflection film, but also the polymerizable functional    group of the binder compound is polymerized in the antireflection    film).-   (3) Silanol group-containing silicon compounds, such as silicic    acid, trimethylsilanol, triphenylsilanol, dimethylsilanediol    diphenylsilanediol, silanol-terminated polydimethylsiloxane,    silanol-terminated polydiphenylsiloxane, silanol-terminated    polymethylphenylsiloxane, silanol-terminated polymethyl ladder    siloxane, silanol-terminated polyphenyl ladder siloxane and    octahydroxyoctasilsesquioxane (wherein when any one of these    compounds exemplified in this item (3) is used as a binder compound,    it is preferred that the binder compound is three-dimensionally    cross-linked through siloxane linkages in the antireflection film).-   (4) Activated silica, which can be obtained by contacting the    below-mentioned silicates with an acid or an ion exchange resin:    water glass, sodium orthosilicate, potassium orthosilicate, lithium    orthosilicate, sodium metasilicate, potassium metasilicate, lithium    metasilicate, tetramethylammonium orthosilicate, tetrapropylammonium    orthosilicate, tetramethylammonium metasilicate, tetrapropylammonium    metasilicate and the like (wherein when any one of these compounds    exemplified in this item (4) is used as a binder compound, it is    preferred that the binder compound is three-dimensionally    cross-linked through siloxane linkages in the antireflection film).-   (5) Organic polymers, such as polyethers (e.g., polyethylene glycol,    polypropylene glycol and polytetramethylene glycol), amides (e.g., a    polyacrylamide derivative, a polymethacrylamide derivative,    poly(N-vinylpyrrolidone) and poly(N-acylethyleneimene)), esters    (e.g., a polyvinyl alcohol, a polyvinyl acetate, a polyacrylic acid    derivative, a polymethacrylic acid derivative and polycaprolactone),    polyimides, polyurethanes, polyureas and polycarbonates (wherein    when these organic polymers have a polymerizable functional group at    a terminal thereof or in the main chain thereof, it is preferred    that the polymerizable functional group is polymerized in the    antireflection film).-   (6) Polymerizable monomers, such as alkyl(meth)acrylate, alkylene    bis(meth)acrylate, trimethylolpropane tri(meth)acrylate,    pentaerythritol tri(meth)acrylate, pentaerythritol    tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate,    dipentaerythritol hexa(meth)acrylate, alkylene bisglycidyl ether,    trimethylolpropane triglycidyl ether, pentaerythritol triglycidyl    ether, pentaerythritol tetraglycidyl ether and vinylcyclohexene    diepoxide (the term “(meth)acrylate” means both an acrylate and a    methacrylate) (wherein when any one of these compounds exemplified    in this item (6) is used as a binder compound, it is preferred that    the binder compound is cured in the antireflection film).-   (7) Conventional curable resins, such as a (meth)acrylic UV-curable    resin, a moisture-curable silicone resin, a heat-curable silicone    resin, an epoxy resin, a phenoxy resin, a novolac resin, a silicone    acrylate resin, a melamine resin, a phenol resin, an unsaturated    polyester resin, a polyimide resin, a urethane resin and a urea    resin (wherein when any one of these compounds exemplified in this    item (7) is used as a binder compound, it is preferred that the    binder compound is three-dimensionally cross-linked through siloxane    linkages or that the polymerizable functional group of the binder    compound is polymerized in the antireflection film).

The above-exemplified binder compounds may be used individually or incombination. Among these binder compounds, especially preferred arethose exemplified in item (2) above, i.e., hydrolysable silanes having,in a molecule thereof, a polymerizable functional group and a functionalgroup capable of forming a covalent bond with silica particles. Further,among the organic polymers exemplified in item (5) above, those whichhave a polymerizable functional group at a terminal thereof or in themain chain thereof can be preferably used in combination with apolymerizable monomer (exemplified in item (6) above). Especially when acompound exemplified in item (2) above is used as a binder compound, thebinder compound is not only present as a polymer in the antireflectionfilm, but also forms covalent bonds with silica particles, therebyrendering it possible to obtain an antireflection film having moreexcellent mechanical properties. Even when a binder compound which doesnot form covalent bonds with silica particles is used, the bindercompound bonds to silica particles by an intermolecular force, orthrough a hydrogen bond, an ionic bond or the like.

The weight ratio of the binder compound to silica particles is from 0.01to 20, preferably from 0.1 to 10, more preferably from 0.2 to 5, stillmore preferably from 0.3 to 2.

Among the above-exemplified binder compounds, especially preferred arethose exemplified in item (2) above, i.e., hydrolysable silanes having,in a molecule thereof, a polymerizable functional group and a functionalgroup capable of forming a covalent bond with silica particles, or apartial hydrolysis product and/or a dehydration-condensation productthereof. The reasons why these binder compounds exemplified in item (2)are preferred are that by the use of these binder compounds, silicaparticles are easily dispersed uniformly, thereby reducing thearithmetic mean surface roughness (Ra) of the antireflection film, andthat it becomes easier to cause silica particles to be present at aposition near the surface of the antireflection film. With respect tothe content of such a binder compound, the molar ratio of the functionalgroups capable of forming covalent bonds with silica particles to thesilicon atoms present in the silica particles in the antireflection filmis from 0.01 to 5, preferably from 0.05 to 3, still more preferably from0.1 to 1. With respect to counting the number of the functional groupscapable of forming covalent bonds with silica particles, for example,any one of a trimethoxysilyl group, a methyldimethoxysilyl group and adimethylmethoxysilyl group is counted as one group. The same principlealso applies to silyl groups having an ethoxyl group(s), an acetylgroup(s), a chloro group(s) or the like.

The antireflection film of the present invention is obtained bydispersing, in a dispersion medium, the above-mentioned silicaparticles, at least one binder compound and, optionally, an additive,and coating the resultant dispersion onto an optical substrate or aprovisional substrate mentioned below. With respect to the dispersionmedium, there is no particular limitation as long as the silicaparticles, the binder compound and the additive can be substantiallystably dispersed therein.

Specific examples of dispersion media include water; alcohols, such asmonohydric C₁-C₆ alcohols, dihydric C₁-C₆ alcohols and glycerol; amides,such as formamide, N-methylformamide, N-ethylformamide,N,N-dimethylformamide, N,N-diethylformamide, N-methylacetamide,N-ethylacetamide, N,N-dimethylacetamide, N,N-diethylacetamide andN-methylpyrrolidone; ethers, such as tetrahydrofuran, diethyl ether,di(n-propyl)ether, diisopropyl ether, diglyme, 1,4-dioxane, ethyleneglycol dimethyl ether, ethylene glycol diethyl ether and propyleneglycol dimethyl ether; alkanol ethers, such as ethylene glycolmonomethyl ether, propylene glycol monomethyl ether, ethylene glycolmonoethyl ether, propylene glycol monoethyl ether, ethylene glycolmonopropyl ether, propylene glycol monopropyl ether, ethylene glycolmonobutyl ether and propylene glycol monobutyl ether; esters, such asethyl formate, methyl acetate, ethyl acetate, ethyl lactate, ethyleneglycol monomethyl ether acetate, ethylene glycol diacetate, propyleneglycol monomethyl ether acetate, diethyl carbonate, ethylene carbonate,propylene carbonate, γ-butyrolactone and ethyl acetoacetate; ketones,such as acetone, methyl ethyl ketone, methyl propyl ketone,methyl(n-butyl)ketone, methyl isobutyl ketone, methyl amyl ketone,acetyl acetone, cyclopentanone and cyclohexanone; nitriles, such asacetonitrile, propionitrile, n-butyronitrile and isobutyronitrile;dimethyl sulfoxide; dimethyl sulfone; and sulfolane.

Preferred examples of dispersion media include monohydric C₁-C₆alcohols; alkanol ethers, such as ethylene glycol monomethyl ether,propylene glycol monomethyl ether, ethylene glycol monoethyl ether,propylene glycol monoethyl ether, ethylene glycol monopropyl ether,propylene glycol monopropyl ether, ethylene glycol monobutyl ether andpropylene glycol monobutyl ether; and ketones, such as acetone, methylethyl ketone, methyl propyl ketone, methyl(n-butyl)ketone, methylisobutyl ketone, methyl amyl ketone, acetyl acetone, cyclopentanone andcyclohexanone.

These dispersion media may be used in combination, or in mixture withanother appropriate solvent or an additive so long as the effects of thepresent invention are not impaired.

For imparting excellent film-forming ability to the above-mentioneddispersion, it is preferred that the concentration of the silicaparticles is in the range of from 0.01 to 10% by weight, moreadvantageously from 0.05 to 5% by weight. When the concentration of thesilica particles is less than 0.01% by weight, it becomes difficult toobtain a film having a desired thickness. On the other hand, when theconcentration of the silica particles is more than 10% by weight, theviscosity of the dispersion as a coating liquid becomes too high and thefilm-forming ability is likely to become lowered.

Since the above-mentioned dispersion is coated onto an opticalsubstrate, addition of conventional leveling agents and auxiliarybinders (coupling agents) to the dispersion is effective for improvingthe film-forming ability of the dispersion and increasing the adhesionstrength between the final film and the optical substrate.

The binder compound may be coated onto the substrate either by a methodin which a binder compound is added to a dispersion containing silicaparticles (silica particle-containing dispersion) and the resultantdispersion is coated onto a substrate; or by a method in which a bindercompound or a solution thereof is coated onto an optical substrate toform a binder compound layer, and then a silica particle-containingdispersion is coated onto the binder compound layer on the substrate. Inthe latter, the mechanical strength of the final antireflection film canbe improved by causing the binder compound to be well mixed into a partor whole of the silica particle layer which is formed on the bindercompound layer, and good mixing of the binder compound into the silicaparticle layer can be achieved by adjusting the viscosity of the bindercompound, by appropriately selecting the type of the dispersion mediumused for dispersing the silica particles, by adjusting the temperatureand time for the heat treatment performed after the coating step, or byperforming a pressing treatment. Alternatively, the antireflection filmcan be formed by a method in which the order of the coating steps isreversed, that is, by a method in which the dispersion containing thesilica particles is coated onto a substrate to form a silica particlelayer, and then the binder compound or a solution thereof is coated ontothe silica particle layer on the optical substrate. Also in this method,it is preferred to cause the binder compound to be well mixed into apart or whole of the silica particle layer which is formed before thecoating of the binder compound or a solution thereof, and good mixing ofthe binder compound into the silica particle layer can be achieved byadjusting the viscosity of the binder compound, by appropriatelyselecting the type of the dispersion medium used for dispersing thesilica particles, by adjusting the temperature and time for the heattreatment performed after the coating step, or by performing a pressingtreatment.

Further, even when the binder compound is contained in the silicaparticle-containing dispersion and, hence, a silica particle layercontaining a binder compound is obtained, it is possible to separatelyapply a binder compound onto the silica particle layer containing abinder compound. For example, there may be performed a procedure inwhich a silica particle-containing dispersion which also contains ahydrolyzable silane is coated onto a substrate, followed by coating of a(meth)acrylic UV-curable resin.

When the binder compound used is a combination of the polymerizablemonomer (6) above with an organic polymer having a polymerizablefunctional group at a terminal thereof or in the main chain thereof, thelatter being selected from the organic polymer (5) above, the type ofthe polymerizable monomer (6) is appropriately selected in accordancewith the form of the reaction, the reaction rate and the like. Also, itis effective to add, as an additive, a polymerization initiator to thebinder compound. The polymerization initiator may be selected fromconventional polymerization initiators, such as a heat type radicalgenerator, a photo type radical generator, a heat type acid generatorand a photo type acid generator, in accordance with the reaction form ofthe above-mentioned polymerizable functional group or the polymerizablemonomer. Specific examples of heat/photo type radical generators includeacetophenone type polymerization initiators, benzophenone typepolymerization initiators, phosphine oxide type polymerizationinitiators and titanocene type polymerization initiators, which arerepresented by commercially available polymerization initiators, such asIrgacure® series and Dalocure® series (both manufactured and sold byCiba Specialty Chemicals K.K., Japan); thioxanthone type polymerizationinitiators; diazo type polymerization initiators and O-acyl oxime typepolymerization initiators. Among these, especially preferred areIrgacure® 907, Irgacure® 369, Irgacure® 379 and the like which arepolymerization initiators having an amino group and/or a morpholinogroup in the molecule thereof. Specific examples of heat/photo type acidgenerators include sulfonium type polymerization initiators, iodoniumtype polymerization initiators and diazomethane type polymerizationinitiators, which are represented by commercially availablepolymerization initiators, such as San-Aid™ SI series (manufactured andsold by Sanshin Chemical Industry Co., Ltd., Japan), WPI series and WPGAseries (both manufactured and sold by Wako Pure Chemical Industries,Ltd., Japan), and PAGs series (manufactured and sold by SIGMA-ALDRICHJapan, K.K., Japan).

When there is used a binder compound having a polymerizable functionalgroup, such as the hydrolyzable silane compound (2), the polymerizablemonomer (6) or an organic polymer (selected from the organic polymer (5)above) having a polymerizable functional group at a terminal or in themain chain thereof, the binder compound may be polymerized in advance solong as the resultant polymer is capable of being dissolved or dispersedin the above-mentioned dispersion medium. Especially in a case wherebinder compounds having low boiling temperatures are used incombination, when the binder compounds are polymerized in advance, therecan be made an easy adjustment of the uniformity of the film thicknessduring the coating step.

When the hydrolyzable silanes (1) and (2) above are used as the bindercompound, these compounds can be used in a monomeric form, but it ispreferred that the compounds are used after performing partialhydrolysis/dehydration condensation thereof. The partialhydrolysis/dehydration condensation reaction is performed by reactingthe hydrolyzable silanes with water, and a catalyst may be used tocatalyze this reaction. Specific examples of such catalysts includeacids, such as hydrochloric acid, sulfuric acid, nitric acid, phosphoricacid, boric acid, formic acid and acetic acid; alkalis, such as ammonia,trialkylamine, sodium hydroxide, potassium hydroxide, cholines andtetraalkylammonium hydroxides; and tin compounds, such as dibutyltindilaurate. Before the hydrolyzable silane is mixed with the silicaparticles, the former may be subjected to partial hydrolysis/dehydrationcondensation reaction. Alternatively, the partial hydrolysis/dehydrationcondensation reaction of the hydrolyzable silane may be performed in thepresence of silica particles.

The antireflection film of the present invention may contain variousadditives, such as an antistatic agent, an ultraviolet absorber, aninfrared absorber, a leveling agent, a pigment, a metal salt, asurfactant and a mold release agent. The amount of the additives isselected to be in a range which does not impair the effects of thepresent invention. It is preferred that the additives are used in anamount of 100% by weight or less, based on the total weight of thesilica particles and the binder compound.

With respect to the method for producing the antireflection film of thepresent invention, there is no particular limitation, and anyconventional method for forming a film may be employed so long as theshape of the silica particles, the silica particle content, theconcentration of the coating liquid, the type and concentration of thebinder compound, and the type and concentration of the additives, andthe method and conditions for forming a coating are appropriatelyselected when the above-mentioned dispersion containing the silicaparticles and the solution containing the binder compound are appliedonto the optical substrate.

The coating of the silica particle-containing dispersion and the bindercompound-containing solution on a substrate can be performed by anyconventional coating method, such as a dip coating method, a spincoating method, a knife coating method, a bar coating method, a bladecoating method, a squeeze coating method, a reverse-roll coating method,a gravure-roll coating method, a slide coating method, a curtain coatingmethod, a spray coating method, a die coating method or a cap coatingmethod. Among these coating methods, it is preferred to use coatingmethods which can perform continuous coating, such as a knife coatingmethod, a bar coating method, a blade coating method, a squeeze coatingmethod, a reverse-roll coating method, a gravure-roll coating method, aslide coating method, a curtain coating method, a spray coating method,a die coating method and a cap coating method.

After coating the silica particle-containing dispersion and the bindercompound-containing solution on a substrate, it is advantageous tosubject the resultant coating on the substrate to heating, to therebyvolatilize the dispersion medium and perform the condensation andcrosslinking of the silica particles and the binder compound. Thetemperature and time for the heating are determined by the heatresistance of the optical substrate. For example, when a glass substrateis used as the optical substrate, the coating may be heated at 500° C.or higher. On the other hand, when a resin substrate is used as theoptical substrate, the heating temperature is generally in the range offrom 50 to 200° C., preferably from 80 to 150° C., and the heating timeis generally in the range of from 1 second to 1 hour, preferably from 10seconds to 3 minutes. Further, when the binder compound hasradiation-curability, UV irradiation or electron beam irradiation may beperformed by conventional methods.

Further, for the purpose of, e.g., smoothing the surface of theantireflection film and imparting stainproofing property to the surfaceof the antireflection film, an optional overcoat layer may be formed onthe antireflection film. The overcoat layer is formed using aconventional material, such as a fluororesin, a moisture-curablesilicone resin, a heat-curable silicone resin, silicon dioxide, a(meth)acryl resin, a (meth)acryl UV curable resin, an epoxy resin, aphenoxy resin, a novolac resin, a silicone acrylate resin, a melamineresin, a phenol resin, an unsaturated polyester resin, a polyimideresin, a urethane resin and a urea resin. The thickness of the overcoatlayer is generally 50 nm or less, preferably 30 nm or less, morepreferably 15 nm or less, most preferably 6 nm or less. The overcoatlayer may be composed of a single layer or multiple layers. Among theabove-mentioned resins, for imparting stainproofing properties, afluororesin, a moisture-curable silicone resin and a heat-curablesilicone resin are preferred.

When the above-mentioned overcoat layer is formed on the surface of theantireflection film, the arithmetic mean surface roughness and thesilicon atom content of the surface of the antireflection film aremeasured with respect to the surface of the overcoat layer as theuppermost layer of the antireflection film. When the overcoat layer isformed on the surface of an antireflection film, in general, a overcoatlayer is formed on an antireflection film having an arithmetic meansurface roughness (Ra) of not more than 2 nm and a silicon atom contentof 10 atom % or more, wherein these characteristics of theantireflection film are maintained even after the formation of theovercoat layer, for example by adjusting the thickness of the overcoatlayer to a satisfactorily small value.

The antireflection film of the present invention has an arithmetic meansurface roughness (Ra) of not more than 2 nm, preferably not more than1.5 nm, more preferably not more than 1 nm. When the arithmetic meansurface roughness (Ra) exceeds 2 nm, the abrasion resistance becomeslowered drastically. The arithmetic mean surface roughness (Ra) ismeasured using the below-mentioned scanning probe microscope.

In the present invention, the silicon atom content, as measured by X-rayphotoelectron spectroscopy (XPS) with respect to the surface of theantireflection film, is 10 atom % or more, preferably 15 atom % or more.When the silicon atom content is less than 10 atom %, the surfacehardness of the film becomes unsatisfactory and the abrasion resistancemay become lowered.

During the measurement of the silicon atom content by X-rayphotoelectron spectroscopy (XPS), the detected atoms are present at adepth of from about 1 to 10 nm from the surface of the antireflectionfilm. The conditions for the XPS are as follows.

Apparatus: ESCALAB 250 (manufactured and sold by Thermo Electron K.K.,Japan)

X-ray source: monochromatized AlKα 15 kV×10 mA

Analyzed area: oval shape (300 μm×600 μm)

Method for measurement: Survey Scan

Scanning range: 1,100 to 0 eV (C1S, O1s, Si2p)

Pass Energy: 100 eV

In the present invention, during the measurement of the arithmetic meansurface roughness (Ra) and the silicon atom content, the point ofmeasurement must be selected with care. This is because when the pointof measurement is selected randomly, the measurement may be made withrespect to an atypical point, such as an impurity, an agglomerate or apinhole, and such measurement lowers the reliability of the obtainedvalue. For obtaining a reliable value, for example, the measurement ofthe arithmetic mean surface roughness (Ra) can be performed by obtainingan image of a large area of the antireflection film; selecting severalpoints of measurement from typical portions containing no impurities,agglomerates or pinholes; and taking a mean of the measured values tothereby obtain an arithmetic mean surface roughness (Ra). The sameapplies to the measurement of the silicon atom content. In general,several points of measurement are selected visually from typicalportions containing no impurities, agglomerates or pinholes and, then,an average of the measured values is determined to thereby obtain asilicon atom content. Since substantially the same value is generallyobtained for all points of measurement which are selected in theabove-mentioned manner, even a value obtained from only one point ofmeasurement is considered to be a satisfactorily reliable value.

The antireflection film of the present invention has a very smoothsurface structure with only very small unevenness even when its siliconatom content is 100 atom % or a value close to 100 atom %. Despite ofsuch a smooth surface structure, the antireflection film of the presentinvention has excellent abrasion resistance. It is considered that theexcellent abrasion resistance of the antireflection film is imparted bythe unique properties that the antireflection film exhibits not onlyvery high surface hardness, but also other excellent properties that thesilica particles present at the surface do not come off upon abrasion,and stress is not concentrated on a local point.

As explained above, conventionally, when the silica content of anantireflection film is increased to improve the antireflectionproperties and strength, a problem arises in that the abrasionresistance of the antireflection film becomes lowered. However, thepresent invention solves this problem by adjusting the silica particlecontent of the antireflection film to 30% by weight or more whilemaintaining the arithmetic mean roughness and the silicon atom contentof the surface of the antireflection film within specific ranges.

Pores are not necessary in the antireflection film, but pores may beformed in the antireflection film for adjusting the refractive index ofthe film. The porosity is 0 to 70% by volume, preferably 1 to 60% byvolume, more preferably 3 to 50% by volume, based on the volume of theantireflection film. When the porosity exceeds 70% by volume, thestrength of the antireflection film becomes lowered. The porosity may beadjusted by selecting the form and amount of the silica particles andthe type and amount of the binder compound used. It is desired that therefractive index of the antireflection film is adjusted within the rangeof from 1.22 to 1.55. The porosity can be calculated from the refractiveindex measured using a spectrophotometer.

In the present invention, 2 or more antireflection films may belaminated.

Further, the antireflection film of the present invention can belaminated directly or indirectly on a high refraction film which has arefractive index higher than the refractive index of the antireflectionfilm, thereby obtaining an antireflection laminate film. Such anantireflection laminate film is preferred because it exhibits higherantireflection effects. The expression “laminating an antireflectionfilm indirectly on a high refraction film” means that a predeterminedlayer (such as an antistatic layer or a hard coat layer explained below)having a thickness which does not impair the effects of theantireflection film is provided between the antireflection film and thehigh refraction film.

As the high refraction film, there can be used a film comprisingconventional inorganic particles and a binder compound which binds theinorganic particles together. Examples of inorganic particles includeparticles of metal oxides or complex metal oxides comprising at leastone metal selected from the group consisting of titanium, zirconium,zinc, cerium, tantalum, yttrium, hafnium, aluminum, magnesium, indium,tin, molybdenum, antimony and gallium. Among the above-mentioned metaloxides, zirconium oxide having high refractive index and lightresistance is preferred. As the binder compound, there can be used thecompounds (1) to (7) above which are exemplified as the binder compoundsused for the antireflection film of the present invention. Among these,preferred are the hydrolyzable silane compound (2) having in themolecule thereof a polymerizable functional group and a functional groupcapable of covalently bonding to a silica particle, an organic polymer(selected form the organic polymer (5)) having a polymerizablefunctional group at a terminal or in the main chain thereof, thepolymerizable monomer (6) and the curable resin (7). The type and amountof the binder compound are selected in accordance with the desiredrefractive index, strength, light resistance, yellowing resistance andthe like, and conventional binder compounds may be used. The refractiveindex of the high refraction film is in the range of from 1.4 to 2.5,preferably from 1.55 to 2.5, more preferably from 1.6 to 1.9, and thethickness of the high refraction film is in the range of from 0.01 to 1μm, preferably from 0.03 to 0.5 μm, more preferably from 0.05 to 0.2 μm.The refractive index and thickness of the high refraction film areselected in accordance with the refractive index and thickness of theantireflection film, the refractive index of the optical substrate, andthe refractive index and thickness of other layers present in theantireflection laminate film. A laminate film, such as explained above,can be used advantageously as an antireflection film for opticalsubstrates having various refractive indices.

Further, in the present invention, an antistatic layer provided belowthe antireflection film or the antireflection laminate film (that is, atthe side facing the optical substrate) or provided between theantireflection film and the high refraction film, is advantageous forpreventing dust from attaching to the antireflection film or theantireflection laminate film. As the antistatic layer, there can be usedconventional antistatic agents, such as a surfactant and an ionicpolymer; or a dispersion of conductive microparticles in a bindercompound. Conventional conductive particles can be used as theconductive microparticles, and specific examples of conventionalconductive particles include microparticles of oxides or complex oxidescontaining indium, zinc, tin, molybdenum, antimony or gallium;microparticles of metals, such as copper, silver, nickel and low meltingpoint alloys (such as solder); polymeric microparticles coated with ametal; carbon blacks; conductive polymer particles, such as polypyrroleand polyaniline; metal fibers and carbon fibers. Among these, indium tinoxide (ITO) particles and antimony tin oxide (ATO) particles, both ofwhich impart high transparency and conductivity, are preferred. Thethickness of the antistatic layer is generally in the range of from 0.01to 1 μm, preferably from 0.03 to 0.5 μm, most preferably from 0.05 to0.2 μm. With respect to the binder compound contained in the antistaticlayer, there can be used the compounds (1) to (7) above which areexemplified as the binder compounds used for the antireflection film ofthe present invention. Among these, preferred are thehydrolyzable-silane compound (2) having in the molecule thereof apolymerizable functional group and a functional group capable ofcovalently bonding to a silica particle, an organic polymer (selectedfrom the organic polymer (5)) having a polymerizable functional group ata terminal or in the main chain thereof, the polymerizable monomer (6)and the curable resin (7).

In the present invention, a hard coat layer provided below theantireflection film or the antireflection laminate film, or providedbetween the antireflection film and the high refraction film ispreferred for improving the pencil hardness and the impact resistance ofthe antireflection film or the antireflection laminate film. When anantistatic layer is provided, the hard coat layer is provided below theantistatic layer. A hard coat layer is formed by coating a conventionalhard coat layer-forming material, such as a silicone material, a(meth)acrylic material, an epoxy material, a urethane material, an epoxyacrylate material and a urethane acrylate material. In addition, thehard coat layer can also be formed by coating a coating liquid whichcontains a multifunctional monomer and the like together with apolymerization initiator, wherein, after the coating of the coatingliquid, the multifunctional monomer is caused to be polymerized, therebyforming a hard coat layer. The thickness of the hard coat layer isgenerally in the range of from 0.1 to 10 μm, preferably from 0.5 to 8μm. more preferably from 1 to 6 μm, most preferably from 2 to 5 μm.

In the above-mentioned antistatic laminate film, two or all of thefunctions of the high refraction film, the antistatic layer and the hardcoat layer may be carried by a single layer. For example, a layercontaining a high refraction material and a conductive material may beprovided as a high refraction layer having antistatic effect, and aconductive material may be added to the hard coat-forming material, soas to form an antistatic hard coat layer. The thickness of such anantistatic hard coat layer should be in the range which is describedabove for the (non-antistatic) hard coat layer.

Further, two or more layers of each of the antireflection film, the highrefraction film, the antistatic layer and the hard coat layer may bepresent in the above-mentioned antireflection laminate film.

The antireflection film and the antireflection laminate film of thepresent invention can be advantageously used in the form of the opticalpart of the present invention which comprises an optical substrate and,laminated thereon, the antireflection film or the antireflectionlaminate film of the present invention. The optical part of the presentinvention exhibits excellent antireflection performance.

Specific examples of optical substrates used in the optical part of thepresent invention include a glass plate; various resin plates, resinsheets and resin films, such as a (meth)acrylic resin plate, a(meth)acrylic resin sheet, a styrene/methyl(meth)acrylate copolymerresin plate, a styrene/methyl(meth)acrylate copolymer resin sheet, apolyethylene film, a polypropylene film, cellulose acetate type filmsincluding a triacetyl cellulose film and a cellulose acetate propionatefilm, stretched polyester films including stretched films ofpolyethylene terephthalate and polyethylene naphthalate, polycarbonatefilms, norbornene films, polyarylate films and polysulfone films;optical substrates used in various application fields, such as thefields of eyesight-correcting articles (e.g., lenses of eye-glasses,lenses of goggles and contact lenses), automobiles (e.g., windows of anautomobile, instrumental panels and a navigation system), housing andbuilding (e.g., windowpane), agro-industrial products (e.g., alight-transmitting film or sheet for a plastic greenhouse), batteries(e.g., solar battery and photoelectric cell), electronic informationappliances (e.g., a cathode-ray tube, a plasma display panel, a notebookcomputer, an electronic organizer, a touch screen, a liquid crystaldisplay (LCD) television, an LCD monitor, an in-vehicle TV, an LCDcamcorder, a projection television, an optical fiber and an opticaldisc), household articles (e.g., a lighting globe, a fluorescent light,a mirror and a clock), business articles (e.g., a showcase, a pictureframe, semiconductor lithography and a copying machine), and amusementarticles (e.g., a liquid crystal display game machine, a glass lid of apinball machine, and game machines). All of these are light-transmittingoptical substrates, which are required to be free from glaring and/or tohave improved light transmittance.

With respect to the method for producing the optical part of the presentinvention, there is no particular limitation. However, when the opticalpart of the present invention is produced by using the below-mentionedtransfer foil, there is an advantage in that the optical part having anantireflection film having an arithmetic mean surface roughness (Ra) ofnot more than 2 nm can be produced with ease. Alternatively, the opticalpart comprising an antireflection film having an arithmetic mean surfaceroughness (Ra) of not more than 2 nm can also be produced without usinga transfer foil, but by employing a method in which an antireflectionfilm is laminated onto an optical substrate directly or, if desired,indirectly through a hard coat layer, an antistatic layer and a highrefraction film which are previously formed on the optical substrate.However, when an antireflection film is produced without the use of atransfer foil, it sometimes becomes difficult to satisfactorily increasethe silicon atom content of the surface of the antireflection filmbecause in general, silica particles have a specific gravity and asurface energy which are larger than those of a binder compound, so thatthe silica particles easily sink into the inner portion of theantireflection film. In addition, in the case where an antireflectionfilm is laminated on top of a plurality of layers laminated on anoptical substrate to thereby form an optical part, it sometimes becomesdifficult to cause the antireflection film to have a small value of thearithmetic mean surface roughness (Ra) because in general, thenon-uniformity in thickness and the dents and bumps of each layer becomemarkedly accumulated in accordance with the increase in the number oflayers laminated.

Hereinbelow, specific explanations are given with respect to the methodfor producing the antireflection film and the antireflection laminatefilm by using a transfer foil.

The transfer foil comprises a provisional substrate and, laminatedthereon, the antireflection film or antireflection laminate film of thepresent invention. The transfer foil is used in a procedure whichcomprises the steps of: laminating the transfer foil on an opticalsubstrate so that the surface (i.e., the antireflection film layer) ofthe transfer foil which is remote from the provisional substrate layerfaces the optical substrate; and delaminating the provisional substratelayer of the transfer foil to thereby transfer the antireflection filmor antireflection laminate film onto the optical substrate.

With respect to the material for the provisional substrate, there is noparticular limitation, and any desired substrate can be used. Forexample, there can be used a glass plate, a metal plate, a (meth)acrylicresin sheet, a polyethylene film, a polypropylene film, celluloseacetate type films including a triacetyl cellulose film and a celluloseacetate propionate film, stretched polyester films including stretchedfilms of polyethylene terephthalate and polyethylene naphthalate,polycarbonate films, norbornene films, polyarylate films and polysulfonefilms.

When using these provisional substrates, it is preferred that thesurface thereof is as smooth as possible. For improving the smoothnessof the surface of a provisional substrate, it is useful to subject theprovisional substrate to a process for forming thereon theabove-mentioned hard coat layer.

For improving the releasability between the provisional substrate andthe antireflection film, there can be used a release layer sandwichedbetween the provisional substrate and the antireflection film. Withrespect to the material for the release layer, there is no particularlimitation, and there can be used any conventional material, such as afluororesin, a silicone resin, a (meth)acrylic resin and a melamineresin.

The arithmetic mean surface roughness (Ra) of the antireflection film ofthe present invention can be adjusted by appropriately controlling thewettability and adhesion property of the provisional substrate or therelease layer with respect to the surface thereof to be adhered to theantireflection film. Specifically, for example, when a provisionalsubstrate (e.g., a fluororesin) having a low surface energy is used, byemploying a solvent or an additive each capable of lowering the surfaceenergy of a coating composition for producing the antireflection film,the wettability of the provisional substrate or the release layer (withrespect to the surface thereof to be adhered to the antireflection film)can be improved, thereby lowering the arithmetic mean surface roughness(Ra) of the antireflection film. On the other hand, when a lowrefraction layer (i.e., an antireflection film) having a relativelylarge (meth)acryl group content is used, by employing a release layerhaving a relatively small (meth)acryl group content, the adhesionstrength of the release layer can be controlled to an appropriate level,thereby facilitating the release of the antireflection film and, hence,enabling a reduction in the arithmetic mean surface roughness (Ra) ofthe antireflection film.

The above-mentioned provisional substrate is coated with theabove-mentioned coating composition containing silica particles, tothereby form an antireflection film thereon and obtain a transfer foil.If desired, optional layers, such as the above-mentioned high refractionfilm, antistatic layer and hard coat layer, may be laminated onto theantireflection film. In this case, by employing a hard coat layer havinga satisfactory mechanical strength, an antireflection film having animproved mechanical strength can be obtained. Further, still other typesof optional layers, such as a dye-containing layer and a UVabsorber-containing layer, may be laminated onto the antireflection filmas long as the effects of the present invention are not impaired.

The thus obtained transfer foil containing the antireflection film islaminated onto an optical substrate so that the antireflection filmfaces the optical substrate, followed by delamination of the provisionalsubstrate, to thereby obtain an optical part. As an optical substrate,any of those exemplified above can be employed. If desired, variousfunctional layers, such as a UV-absorbing layer, an electromagneticwave-insulating layer, an infrared light-absorbing layer, ashock-absorbing layer and a toning layer, may be laminated on theoptical substrate.

The lamination of the transfer foil onto the optical substrate isperformed by adhering the transfer foil onto the optical substratethrough an adhesive layer so that the surface (i.e., the antireflectionfilm layer) of the transfer foil which is remote from the provisionalsubstrate layer faces the optical substrate. With respect to the type ofthe adhesive layer, there is no particular limitation, and anyconventional adhesive material, such as a glue, an adhesive sheet, athermoplastic resin, a thermosetting resin or a radiation curable resincan be used, as long as the material is capable of adhering the opticalsubstrate and the transfer foil to each other. From the viewpoint ofimproving the optical properties, it is preferred that the adhesivelayer is transparent to visible light. With respect to the method foradhering the transfer foil onto the optical substrate, there is noparticular limitation. Examples of methods for adhering include a methodin which an adhesive is applied only onto a surface of the transferfoil, followed by lamination of the transfer foil onto the opticalsubstrate, a method in which an adhesive is applied only onto a surfaceof the optical substrate, followed by lamination of the transfer foilonto the optical substrate, a method in which an adhesive is appliedonto both of a surface of the transfer foil and a surface of the opticalsubstrate, followed by lamination of the transfer foil onto the opticalsubstrate, and a method in which an adhesive sheet is sandwiched betweenthe transfer foil and the optical substrate to form a laminate.

After the transfer foil and the optical substrate are adhered to eachother, the provisional substrate (together with a release layer if any)of the transfer foil is delaminated from the antireflection film of thetransfer foil, thereby obtaining an optical part in which anantireflection film or antireflection laminate film is laminated on anoptical substrate. In the case where a release layer is used, it ispossible that, after the delamination of the release layer from theantireflection film, a residual portion of the release layer remains onthe surface of the antireflection film or has penetrated and migratedinto the surface portion of the antireflection film. Such a residualportion of the release layer may be left as it is, as long as theproperties of the antireflection film suffer substantially no adverseeffects; however, when there is a possibility that the properties of theantireflection film are adversely affected, such a residual portion ofthe release layer should be removed by washing with water or a solvent,wiping-off, heating, etching, ozonation or the like.

The optical part obtained by the above-mentioned method not only has avery smooth surface but also exhibits excellent abrasion resistance.

The antireflection film and the antireflection laminate film of thepresent invention can be formed on various types of optical substrates.In general, especially when the optical part of the present invention isproduced by using the above-mentioned transfer foil, the antireflectionfilm of the present invention can be formed on an optical substrate at atemperature in the range of from room temperature to 200° C. Therefore,the antireflection film of the present invention can be advantageouslyused especially for producing an optical part comprising a resinsubstrate having a low heat resistance and, laminated thereon, anantireflection film.

The optical part of the present invention has a minimum reflectance ofnot more than 2% within the visible light range. Therefore, forproducing the optical part of the present invention, it is preferredthat the thickness and refractive index of the antireflection film andthe refractive index of layers other than the antireflection film arecontrolled so that the obtained optical part exhibits a minimumreflectance within the above-mentioned range. When the optical part hasa minimum reflectance of more than 2% within the visible light range, itbecomes difficult to perceive, with the naked eye, the effects obtainedby forming the antireflection film of the present invention on theoptical substrate.

The optical part of the present invention can achieve a maximumantireflection effect when the thickness and refractive index of theantireflection film (and the high refraction film if any) are controlledso that the obtained optical part exhibits a minimum refractive index ata wavelength of around 550 nm. Depending on the desired use of theoptical part, the wavelength at which the optical part exhibits aminimum refractive index can be arbitrarily chosen. Specifically, forexample, when the thickness and refractive index of the antireflectionfilm are controlled so that the obtained optical part exhibits a minimumrefractive index at a relatively short wavelength, the antireflectionfilm assumes a reddish brown color to the naked eye. On the other hand,when the thickness and refractive index of the antireflection film arecontrolled so that the obtained optical part exhibits a minimumrefractive index at a relatively long wavelength, the antireflectionfilm assumes a blue color to the naked eye.

It is preferred that the optical part of the present invention whichcontains the antireflection film or the antireflection laminate film ofthe present invention has a pencil hardness of H or more, moreadvantageously 2H or more, most advantageously 3H or more. When theoptical part of the present invention has a pencil hardness of H ormore, the optical part can be advantageously used in the field of touchscreens or the like which are frequently hit by, e.g., a finger or astylus. Thus the application field of the optical part of the presentinvention expands. The pencil hardness of the optical part can beimproved by optimizing the type and amount of the silica particles andthe binder compound contained in the antireflection film. Alternatively,the pencil hardness of the optical part can also be improved by makingappropriate selection of a hard coat layer or optical substrate underthe antireflection film.

According to the present invention, it becomes possible to obtain anantireflection film having excellent abrasion resistance and arefletance of not more than 2%, most likely not more than 1%. Therefore,the antireflection film of the present invention and the optical partcontaining the same can be used in a considerably wide variety ofapplication fields, such as the fields of a cathode-ray tube, an LCDmonitor, a plasma display panel, a touch screen, a solar battery,windows of an automobile or a house, lenses of eyeglasses, and ashowcase.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Synthesis Examples, Examples and ComparativeExamples which should not be construed as limiting the scope of thepresent invention.

In the following Synthesis Examples, Examples and Comparative Examples,various measurements of the properties of the obtained antireflectionfilms (or optical parts) were performed by the following methods.

(1) Evaluation of Arithmetic Mean Surface Roughness (Ra) Using aScanning Probe Microscope

The evaluation of the arithmetic mean surface roughness (Ra) wasperformed under the following conditions:

Apparatus: NanoScope® IIIa (manufactured and sold by Digital InstrumentsInc., U.S.A.)

Cantilever: silicon single-crystal probe (model name: NCH-10T;manufactured and sold by NanoWorld AG, Switzerland)

Mode: tapping

Scan size: 1.0 μm

Scan rate: 1.0 Hz

Tip velocity: 2.0 μm/s

Set point: 1.5

Integral gain: 0.46

Proportional gain: 1.3

Image processing: flattening was performed at a flatten order of 0,thereby calibrating the image in the vertical direction thereof.

(2) Measurement of Silicon atom Content by X-ray PhotoelectronSpectroscopy (XPS)

The silicon atom content was measured under the following conditions:

Apparatus: ESCALAB 250 (manufactured and sold by Thermo Electron K.K.,Japan)

X-ray source: monochromatized AlKα 15 kV×10 mA

Analyzed area: oval shape (300 μm×600 μm)

Method for measurement: Survey Scan

Scanning range: 1,100 to 0 eV (C1S, O1s, Si2p)

Pass Energy: 100 eV.

(3) Measurement of Minimum Reflectance

Using a reflectance spectrometer (model name: FE-3000; manufactured andsold by Otsuka Electronics Co., Ltd., Japan), a reflectance spectrum(within the wavelength range of from 250 to 800 nm) of an optical partwas obtained. The minimum value of reflectance in the reflectancespectrum was defined as the minimum reflectance of the optical part.

(4) Abrasion Resistance Test

The abrasion resistance was evaluated using a surface property testingmachine (manufactured and sold by Imoto Machinery Co., Ltd., Japan),equipped with a stainless steel reciprocation rod having a diameter of15 mm. Specifically, a steel wool (trade name: BONSTAR® #0000;manufactured and sold by Nihon Steel Wool K.K., Japan) was secured tothe lower end of the reciprocation rod of the surface property testingmachine, and the steel wool at the lower end of the rod was placed incontact with the surface of an antireflection film, whereupon thereciprocation rod having the steel wool at its lower end was actuated sothat the steel wool was moved back and forth 10 times on the surface ofthe antireflection film while keeping the steel wool under a load of 200g. Then, abrasion marks on the surface of the antireflection film werevisually observed.

(5) Pencil Hardness

The pencil hardness was measured in accordance with JIS K5400, under aload of 1 kg.

SYNTHESIS EXAMPLE 1

89.1 g of an aqueous dispersion of moniliform silica strings which eachcomprise primary silica particles having an average particle diameter ofabout 12 nm and which have an average length of about 100 nm (tradename: Snowtex® OUP; manufactured and sold by Nissan Chemical Industries,Ltd., Japan) (solid silica content: 15.5% by weight), 68.1 g of a silicasol containing spherical silica particles having an average particlediameter of about 10 nm (trade name: Snowtex® OS; manufactured and soldby Nissan Chemical Industries, Ltd., Japan) (solid silica content: 20.3%by weight)) and 75.7 g of ethanol were mixed together at roomtemperature, and 17.1 g of 3-methacryloxypropyltrimethoxysilane (tradename: Sila-Ace; manufactured and sold by Chisso Corporation, Japan) wasadded thereto. The resultant mixture was stirred at 25° C. for 4 hoursto effect a reaction, thereby obtaining a reaction mixture. On the otherhand, 2 g of Irgacure® 369 (manufactured and sold by Ciba SpecialtyChemicals, Japan) and 252 g of ethanol were mixed together to obtain asolution. Then, the obtained solution was added to 200 g of theabove-obtained reaction mixture, and the resultant was stirred at roomtemperature for 5 minutes, thereby obtaining a solution having a solidscontent of 7.5% by weight. The obtained solution having a solids contentof 7.5% by weight was diluted with isopropyl alcohol so as to reduce thesolids content thereof to 3.4% by weight, thereby obtaining coatingcomposition A for forming a low refraction layer.

SYNTHESIS EXAMPLE 2

92.9 g of a dispersion of tin-containing indium oxide particles (tradename: ELCOM V-2506; manufactured and sold by Catalysts & ChemicalsIndustries Co., Ltd., Japan) (solids content: 20.5% by weight) and 125.3g of a dispersion of zinc oxide particles (trade name: ZNAP15WT %-G0;manufactured and sold by C. I. KASEI CO., LTD., Japan) were mixedtogether to obtain a mixture. On the other hand, 304.2 g of isopropylalcohol, 33.8 g of ethylene glycol monobutyl ether and 23.9 g of waterwere mixed together to obtain a mixed solvent. Further, 9.9 g of anacrylic ultraviolet-curable resin (trade name: SANRAD™ RC-600;manufactured and sold by Sanyo Chemical Industries, Ltd., Japan) and 9.9g of methyl ethyl ketone were mixed together to obtain a solution. Then,to the above-obtained mixture of a dispersion of tin-containing indiumoxide particles and a dispersion of zinc oxide particles were added theabove-obtained mixed solvent and the above-obtained solution in thisorder, and the resultant was stirred at room temperature, therebyobtaining a solution having a solids content of 8.0% by weight. Then,the obtained solution was diluted with a mixed solvent comprisingisopropyl alcohol and ethylene glycol monobutyl ether (“isopropylalcohol/ethylene glycol monobutyl ether” weight ratio: 9/1) so as toreduce the solids content of the solution to 6.0% by weight, therebyobtaining coating composition B for forming a high refraction layerhaving an antistatic effect.

EXAMPLE 1

The transfer foil C shown in FIG. 1 was produced as follows.

A surface of a biaxially oriented polyethylene terephthalate film(provisional substrate) 1 (thickness: 50 μm) was coated with a 50% byweight methyl ethyl ketone solution of an acrylic UV curable resin(solids content: 100% by weight) (SANRAD (tradename) RC-600;manufactured and sold by Sanyo Chemical Industries, Ltd., Japan) using abar coater (equipped with #7 rod; manufactured and sold by R. D.Specialties, Inc., U.S.A.). Then, the resultant coating on thepolyethylene terephthalate film was cured by irradiating ultravioletrays (integrated optical power: 250 mJ/cm²) using a UV curing machine(LC-6B type; manufactured and sold by Fusion UV Systems Japan K.K.,Japan) under conditions wherein the intensity is 180 W, the rate of theconveyer is 12 m/minute and the distance from the light source is 53 mm.This UV irradiation operation was performed three times, thereby formingrelease layer 2 on the provisional substrate.

Composition A for forming a low refraction layer was coated on theabove-mentioned release layer 2 using a bar coater (equipped with #4rod; manufactured and sold by R. D. Specialties, Inc., U.S.A.), followedby heat drying at 120° C. for 2 minutes in a recirculating, hot airdryer. Then, the resultant dried coating was cured by irradiatingultraviolet rays (integrated optical power: 250 mJ/cm²) using a UVcuring machine (LC-6B type; manufactured and sold by Fusion UV SystemsJapan K.K., Japan) under conditions wherein the intensity is 180 W, therate of the conveyer is 12 m/minute and the distance from the lightsource is 53 mm. This UV irradiation operation was performed threetimes, thereby forming low refraction layer (antireflection film) 3 onrelease layer 2.

Composition B for forming a high refraction layer having an antistaticeffect was coated on the above-mentioned antireflection film 3 using abar coater (equipped with #4 rod; manufactured and sold by R. D.Specialties, Inc., U.S.A.). Then, the resultant coating was cured byirradiating ultraviolet rays (integrated optical power: 250 mJ/cm²)using a UV curing machine (LC-6B type; manufactured and sold by FusionUV Systems Japan K.K., Japan) under conditions wherein the intensity is180 W, the rate of the conveyer is 12 m/minute and the distance from thelight source is 53 mm. This UV irradiation operation was performed threetimes, thereby forming high refraction layer (high refraction film) 4 onantireflection layer 3.

Subsequently, urethane acrylate hard coat layer 5 (thickness: 5 μm) andthermoplastic urethane adhesive layer 6 (thickness: 2 μm) were formed inthis order on the above-mentioned high refraction layer 4, therebyobtaining transfer foil C.

The obtained transfer foil C was laminated with a 2 mm-thick polymethylmethacrylate-plate 7 (Delaglass® A; manufactured and sold by Asahi KaseiChemicals Corporation, Japan) (optical substrate) so that adhesive layer6 of the transfer foil C was placed in contact with polymethylmethacrylate plate 7, and the resultant was subjected to a rollingtreatment using a laminator (MA II-550 type; manufactured and sold byTaisei Laminator K.K., Japan) under conditions wherein the rollertemperature is 230° C., the roller pressure is 1 kg and the feeding rateis 0.8 mm/second, to thereby perform a film transfer operation andobtain a laminate. The obtained laminate was cooled to room temperature,and polyethylene terephthalate film 1 and release layer 2 were releasedand removed from the laminate, thereby obtaining optical part D shown inFIG. 2.

The characteristics of the optical part D are as shown in Table 1. Thearithmetic mean surface roughness (Ra) was as small as 0.5 nm and thesilicon atom content was as high as 21.6 atom %. The minimum reflectancewas only 0.82% and exhibited excellent antireflection properties.Further, in the abrasion resistance test, no abrasion marks or nodiscoloration were observed, indicating that the optical part D had highstrength.

COMPARATIVE EXAMPLE 1

Urethane acrylate hard coat layer 5 (thickness: 5 μm) was formed on a 2mm-thick polymethyl methacrylate plate 7 (Delaglass® A; manufactured andsold by Asahi Kasei Chemicals Corporation, Japan) (optical substrate),thereby obtaining a substrate having hard coat layer 5 formed thereon.

Composition B for forming a high refraction layer having an antistaticeffect was coated on the above-mentioned hard coat layer 5 using a barcoater (equipped with #4 rod; manufactured and sold by R. D.Specialties, Inc., U.S.A.). Then, the resultant coating was cured byirradiating ultraviolet rays (integrated optical power: 250 mJ/cm2)using a UV curing machine (LC-6B type; manufactured and sold by FusionUV Systems Japan K.K., Japan) under conditions wherein the intensity is180 W, the rate of the conveyer is 12 m/minute and the distance from thelight source is 53 mm. This UV irradiation operation was performed threetimes, thereby forming high refraction layer 4 having an antistaticeffect, on hard coat layer 5.

Composition A for forming a low refraction layer was coated on theabove-mentioned high refraction layer 4 (having an antistatic effect)using a bar coater (equipped with #4 rod; manufactured and sold by R. D.Specialties, Inc., U.S.A.), followed by heat drying at 120° C. for 2minutes in a recirculating, hot air dryer. Then, the resultant driedcoating was cured by irradiating ultraviolet rays (integrated opticalpower: 250 mJ/cm²) using a UV curing machine (LC-6B type; manufacturedand sold by Fusion UV Systems Japan K. K., Japan) under conditionswherein the intensity is 180 W, the rate of the conveyer is 12 m/minuteand the distance from the light source is 53 mm. This UV irradiationoperation was performed three times to form low refraction layer(antireflection film) 3 on high refraction layer 4, thereby obtainingoptical part E shown in FIG. 3.

The characteristics of the optical part E are as shown in Table 1.Although the silicon atom content was 22.7 atom % which is substantiallythe same as that of the optical part D produced in Example 1, thearithmetic mean surface roughness (Ra) was as large as 2.3 nm. Theminimum reflectance was 0.82%, which is the same as that of the opticalpart D produced in Example 1. However, in the abrasion resistance test,many abrasion marks and discoloration were observed.

SYNTHESIS EXAMPLE 3

2.0 g of an aqueous dispersion of moniliform silica strings which eachcomprise primary silica particles having an average particle diameter ofabout 12 nm and which have an average length of about 100 nm (tradename: Snowtex® OUP; manufactured and sold by Nissan Chemical Industries,Ltd., Japan) (solid silica content: 15.5% by weight) was mixed with 18 gof ethanol at room temperature, to thereby obtain a water/ethanoldispersion of moniliform silica strings which has a solid silica contentof 1.5% by weight. To the obtained water/ethanol dispersion ofmoniliform silica strings was added 0.104 g of tetraethoxysilane and0.015 g of a 1N nitric acid, and the resultant was stirred at roomtemperature overnight, thereby obtaining coating composition F forforming a low refraction layer.

EXAMPLE 2

The transfer foil G shown in FIG. 4 was produced as follows.

A surface of a biaxially oriented polyethylene terephthalate film(provisional substrate) 1 (thickness: 50 μm) was coated with a 50% byweight methyl ethyl ketone solution of an acrylic UV curable resin(solids content: 100% by weight) (SANRAD (tradename) RC-600;manufactured and sold by Sanyo Chemical Industries, Ltd., Japan) using abar coater (equipped with #7 rod; manufactured and sold by R. D.Specialties, Inc., U.S.A.). Then, the resultant coating on thepolyethylene terephthalate film was cured by irradiating ultravioletrays (integrated optical power: 350 mJ/cm²) using a UV curing machine(UVC-2519 type, equipped with a high pressure mercury lamp; manufacturedand sold by Ushio Inc., Japan) under conditions wherein the intensity is160 W, the rate of the conveyer is 4.6 m/minute and the distance fromthe light source is 100 mm. This UV irradiation operation was performedthree times, thereby forming release layer 2 on the provisionalsubstrate. Subsequently, a 1.0% methyl isobutyl ketone solution of afluorine-containing surfactant (Fluorad (tradename) FC-4430;manufactured and sold by Sumitomo 3M, Ltd., Japan) was coated on theabove-mentioned release layer 2 by spin coating at 1000 rpm for 30seconds, followed by heat drying at 120° C. for 2 minutes in arecirculating, hot air dryer, thereby forming fluorine-containingsurfactant layer 8 on release layer 2.

Composition F for forming a low refraction layer was coated on theabove-mentioned fluorine-containing surfactant layer 8 by spin coatingat 1000 rpm for 30 seconds, followed by heat drying at 120° C. for 2minutes in a recirculating, hot air dryer, thereby forming lowrefraction layer (antireflection film) 3 on fluorine-containingsurfactant layer 8.

Subsequently, a 2.0% ethanol dispersion of microparticulate complexoxide of antimony (Celnax® CX-Z401M; manufactured and sold by NISSANCHEMICAL INDUSTRIES, LTD., Japan) was coated on the above-mentioned lowrefraction layer 3 by spin coating at 1000 rpm for 30 seconds, followedby heat drying at 120° C. for 2 minutes in a recirculating, hot airdryer to form a high refraction layer 4 having an antistatic effect,thereby obtaining transfer foil G.

On the other hand, laminate H shown in FIG. 5 was produced as follows.

A surface of a biaxially oriented polyethylene terephthalate film 9(thickness: 188 μm) (Cosmoshine (registered tradename) A4300;manufactured and sold by Toyobo, Ltd., Japan) (optical substrate) wascoated with an acrylic UV curable resin (ACH-01; manufactured and soldby Nippon Kayaku Co., Ltd., Japan) by spin coating at 1000 rpm for 30seconds, followed by heat drying at 120° C. for 1 minute in arecirculating, hot air dryer, thereby forming ultraviolet-curable resinlayer 10 on the optical substrate. The resultant optical substrate wasused as laminate H.

The transfer foil G and the laminate H were laid on each other so thathigh refraction layer 4 (having an antistatic effect) of the transferfoil G was placed in contact with ultraviolet-curable resin layer 10 ofthe laminate H, and the resultant was subjected to contact bonding usinga rubber roller, thereby obtaining a laminate. Subsequently,ultraviolet-curable resin layer 10 of the obtained laminate was cured byirradiating ultraviolet rays (integrated optical power: 350 mJ/cm²)using a UV curing machine (UVC-2519 type, equipped with a high pressuremercury lamp; manufactured and sold by Ushio Inc., Japan) underconditions wherein the intensity is 160 WI the rate of the conveyer is4.6 m/minute and the distance from the light source is 100 mm. This UVirradiation operation was performed three times to cure theultraviolet-curable resin layer 10, thereby obtaining hard coat layer 5(which was an ultraviolet-cured resin layer). Then, polyethyleneterephthalate film 1 (provisional substrate), release layer 2 andfluorine-containing surfactant layer 8, which were contained in thetransfer foil G, were released and removed from the laminate, therebyobtaining optical part I shown in FIG. 6.

The characteristics of the optical part I are as shown in Table 1. Thearithmetic mean surface roughness (Ra) was as small as 0.9 nm and thesilicon atom content was as high as 16.1 atom %. The minimum reflectancewas only 1.00% and exhibited excellent antireflection properties.Further, in the abrasion resistance test, no abrasion marks or nodiscoloration were observed, indicating that the optical part I had highstrength.

COMPARATIVE EXAMPLE 2

The optical part J shown in FIG. 7 was produced as follows.

A surface of a biaxially oriented polyethylene terephthalate film 9(thickness: 188 μm) (Cosmoshine (registered tradename) A4300;manufactured and sold by Toyobo, Ltd., Japan) (optical substrate) wascoated with a 50% by weight methyl ethyl ketone solution of an acrylicUV curable resin (solids content: 100% by weight) (SANRADT RC-600;manufactured and sold by Sanyo Chemical Industries, Ltd., Japan) using abar coater (equipped with #7 rod; manufactured and sold by R. D.Specialties, Inc., U.S.A.). Then, the resultant coating on thepolyethylene terephthalate film was cured by irradiating ultravioletrays (integrated optical power: 350 mJ/cm²) using a UV curing machineequipped with a high-pressure mercury lamp (UVC-2519 type; manufacturedand sold by USHIO INC., Japan) under conditions wherein the intensity is160 W, the rate of the conveyer is 4.6 m/minute and the distance fromthe light source is 100 mm. This UV irradiation operation was performedthree times, thereby forming hard coat layer 5 on the optical substrate.

Coating composition F for forming a low refraction layer was spin-coatedon hard coat layer 5 at room temperature, at 1,000 rpm for 30 seconds.Then, the resultant coating was heat dried at 120° C. for 2 minutes in arecirculating, hot air dryer to obtain low refraction layer(antireflection film) 3 on hard coat layer 5, thereby obtaining opticalpart J.

The characteristics of the optical part J are as shown in Table 1. Thesilicon atom content was as high as 28.3 atom %; however, the arithmeticmean surface roughness (Ra) was as high as 4.0 nm disadvantageously.Further, the minimum reflectance was only 0.20%; however, in theabrasion resistance test, many abrasion marks and discoloration wereobserved.

SYNTHESIS EXAMPLE 4

0.1 g of dipentaerythritol hexaacrylate, 0.025 g of a silica solcontaining silica particles having an average particle diameter ofapproximately from 10 to 20 nm (Snowtex® 0; manufactured and sold byNissan Chemical Industries, Ltd., Japan) (solid silica content: 20% byweight), 0.01 g of Irgacure® 369 (manufactured and sold by CibaSpecialty Chemicals, Japan) and 6.9 g of isopropyl alcohol were mixedtogether while stirring at room temperature for 5 minutes, therebyobtaining a coating composition K for forming a low refraction layer.

COMPARATIVE EXAMPLE 3

The transfer foil L shown in FIG. 8 was produced as follows.

A surface of a biaxially oriented polyethylene terephthalate film(provisional substrate) 1 (trade name: COSMOSHINE ® A4300; manufacturedand sold by Toyobo Co., Ltd., Japan) (thickness: 188 μm) was spin-coatedwith a 50% by weight methyl ethyl ketone solution of an acrylic UVcurable resin (solids content: 100% by weight) (SANRAD^(T)M RC-600;manufactured and sold by Sanyo Chemical Industries, Ltd., Japan) at roomtemperature, at 1,500 rpm for 1 second. Then, the resultant coating onthe polyethylene terephthalate film was cured by irradiating ultravioletrays (integrated optical power: 350 mJ/cm²) using a UV curing machineequipped with a high-pressure mercury lamp (UVC-2519 type; manufacturedand sold by USHIO INC., Japan) under conditions wherein the intensity is160 W, the rate of the conveyer is 4.6 m/minute and the distance fromthe light source is 100 mm. This UV irradiation operation was performedthree times, thereby forming release layer 2 on the provisionalsubstrate.

Release layer 2 was spin-coated with coating composition K for forming alow refraction layer at room temperature, at 1,500 rpm for 1 second,followed by heat drying at 120° C. for 2 minutes in a recirculating, hotair dryer. Then, the resultant coating on release layer 2 was cured byirradiating ultraviolet rays (integrated optical power: 350 mJ/cm²)using a UV curing machine equipped with a high-pressure mercury lamp(UVC-2519 type; manufactured and sold by USHIO INC., Japan) underconditions wherein the intensity is 160 W, the rate of the conveyer is4.6 m/minute and the distance from the light source is 100 mm. This UVirradiation operation was performed three times, thereby forming therebyforming low refraction layer (antireflection film) 3 on release layer 2.

Composition B for forming a high refraction layer having an antistaticeffect was spin-coated on the above-mentioned antireflection film 3 atroom temperature, at 2,300 rpm for 1 second. Then, the resultant coatingon antireflection film 3 was cured by irradiating ultraviolet rays(integrated optical power: 350 mJ/cm²) using a UV curing machineequipped with a high-pressure mercury lamp (UVC-2519 type; manufacturedand sold by USHIO INC., Japan) under conditions wherein the intensity is160 W, the rate of the conveyer is 4.6 m/minute and the distance fromthe light source is 100 mm. This UV irradiation operation was performedthree times, thereby forming, on antireflection film 3, high refractionlayer 4 having an antistatic effect.

The above-mentioned high refraction layer 4 having an antistatic effectwas spin-coated with a 50% by weight methyl ethyl ketone solution of anacrylic UV curable resin (solids content: 100% by weight) (SANRADRC-600; manufactured and sold by Sanyo Chemical Industries, Ltd., Japan)at room temperature, at 1,500 rpm for 1 second to formultraviolet-curable resin layer 10 on high refraction layer 4, therebyobtaining transfer foil L.

On the other hand, laminate M shown in FIG. 9 was produced as follows.

A surface of 2 mm-thick polymethyl methacrylate plate (opticalsubstrate) 7 (Delaglass® A; manufactured and sold by Asahi KaseiChemicals Corporation, Japan) was spin-coated with a 50% by weightmethyl ethyl ketone solution of an acrylic UV curable resin (solidscontent: 100% by weight) (SANRAD (tradename) RC-600; manufactured andsold by Sanyo Chemical Industries, Ltd., Japan) at room temperature, at1,500 rpm for 1 second to form ultraviolet-curable resin layer 10 onpolymethyl methacrylate plate 7, thereby obtaining laminate M.

Subsequently, transfer foil L and laminate M were laid on each other sothat ultraviolet-curable resin layer 10 of transfer foil L was placed incontact with ultraviolet-curable resin layer 10 of polymethylmethacrylate plate 7, and the resultant was subjected to contact bondingusing a rubber roller, to thereby form a laminate having a single,ultraviolet-curable resin layer 10. Then, the ultraviolet-curable resinlayer 10 of the laminate was cured by irradiating ultraviolet rays(integrated optical power: 350 mJ/cm²) using a UV curing machineequipped with a high-pressure mercury lamp (UVC-2519 type; manufacturedand sold by USHIO INC., Japan) under conditions wherein the intensity is160 W, the rate of the conveyer is 4.6 m/minute and the distance fromthe light source is 100 mm. This UV irradiation operation was performedthree times to convert ultraviolet-curable resin layer 10 into hard coatlayer 5. From this laminate, polyethylene terephthalate film 1(provisional substrate) and release layer 2 (on the side of transferfoil L) were released and removed, thereby obtaining optical part Nshown in FIG. 10.

The characteristics of the optical part N are as shown in Table 1. Thearithmetic mean surface roughness (Ra) was as small as 0.9 nm; however,the silicon atom content was as low as 9.2 atom % disadvantageously. Theminimum reflectance was 1.41%. Further, in the abrasion resistance test,no discoloration was observed; however, many abrasion marks wereobserved.

TABLE 1 Wavelength at which the Arithmetic Silicon Minimum reflectancemean atom Reflectance becomes roughness content Pencil (%) minimum (nm)(Ra) (nm) (atom %) Abrasion resistance hardness Example 1 0.82 531 0.521.6 No abrasion marks or no discoloration observed Example 2 1.00 6000.9 16.1 No abrasion marks or no 3H discoloration observed Comp. Ex. 10.82 518 2.3 22.7 Many abrasion marks and discoloration observed Comp.Ex. 2 0.20 450 4.0 28.3 Many abrasion marks and 2H discolorationobserved Comp. Ex. 3 1.41 560 0.9 9.2 No discoloration observed, butmany abrasion marks observed

INDUSTRIAL APPLICABILITY

The antireflection film of the present invention not only exhibitsexcellent antireflection performance, but also has excellent propertieswith respect to mechanical strength and abrasion resistance. Therefore,the antireflection film of the present invention is very advantageousfor coating various optical substrates (such as a cathode-ray tube, anLCD monitor, a plasma display panel, a touch screen, a solar battery,windows of an automobile or a house, lenses of eye-glasses, and ashowcase).

1. An antireflection film comprising silica particles and at least onebinder compound, wherein said silica particles are bound togetherthrough said at least one binder compound, said antireflection filmhaving the following characteristics (a) to (c): (a) a silica particlecontent of 30% by weight or more, based on the weight of theantireflection film, (b) an arithmetic mean surface roughness (Ra) ofnot more than 1.5 nm, (c) a silicon atom content of 10 atom % or more,as measured by X-ray photoelectron spectroscopy (XPS) with respect tothe surface of the antireflection film, and (d) a reflectance of notmore than 1%.
 2. The antireflection film according to claim 1, whereinsaid at least one binder compound is a polymer having functional groups,and wherein said silica particles are covalently bonded to thefunctional groups of said polymer.
 3. The antireflection film accordingto claim 2, wherein the molar ratio of the functional groups of saidpolymer to the silicon atoms present in said silica particles is from0.01 to
 5. 4. The antireflection film according to claim 1, wherein saidsilica particles comprise at least one stringy silica particle selectedfrom the group consisting of a moniliform silica swing and a fibroussilica particle.
 5. The antireflection film according to claim 4,wherein said at least one stringy silica particle is present in anamount of 50% by weight or less, based on the weight of theantireflection film.
 6. The antireflection film according to claim 1,which is porous and has a porosity of from 3 to 50% by volume.
 7. Anantireflection laminate film comprising a high refraction film and,laminated thereon directly or indirectly, the antireflection film of anyone of claims 1 to 6, wherein said high refraction film has a refractiveindex higher than the refractive index of said antireflection film. 8.The antireflection laminate film according to claim 7, wherein said highrefraction film comprises: particles of at least one metal oxidecomprising at least one metal selected from the group consisting oftitanium, zirconium, zinc, cerium, tantalum, yttrium, hafnium, aluminum,magnesium, indium, tin, molybdenum, antimony and gallium, and at leastone binder compound, wherein said particles of at least one metal oxideare bound together through said at least one binder compound.
 9. Anoptical part comprising an optical substrate and, laminated thereon, theantireflection film of any one of claims 1 to
 6. 10. The optical partaccording to claim 9, wherein said optical substrate is a transparentresin substrate.
 11. The optical part according to claim 9, which has aminimum reflectance of not more than 2% within the visible light range.12. The optical part according to claim 9, which has a pencil hardnessof 2H or more.
 13. The optical part according to claim 9, which isobtained by a method comprising: (1) forming the antireflection film ofany one of claims 1 to 6 on a provisional substrate having releasabilitywith respect to said antireflection film, to thereby obtain a laminate(i); (2) laminating an optical substrate on the antireflection film ofsaid laminate (i) to obtain a laminate (ii); and (3) delaminating theprovisional substrate from said laminate (ii) to obtain an optical part.14. An optical part comprising an optical substrate and, laminatedthereon, the antireflection laminate film of claim
 7. 15. The opticalpart according to claim 14, wherein said optical substrate is atransparent resin substrate.
 16. The optical part according to claim 14,which has a minimum reflectance of not more than 2% within the visiblelight range.
 17. The optical part according to claim 14, which has apencil hardness of 2H or more.
 18. The optical part according to claim14, which is obtained by a method comprising: (1) forming theantireflection film of any one of claims 1 to 6 on a provisionalsubstrate having releasability with respect to said antireflection film,to thereby obtain a laminate (I); (2) laminating a high refraction filmon the antireflection film of said laminate (I) to obtain a laminate(II); (3) laminating an optical substrate on the high refraction film ofsaid laminate (II) to obtain a laminate (III); and (4) delaminating theprovisional substrate from said laminate (III) to obtain an opticalpart.